The neuropeptide red pigment concentrating hormone affects rhythmic pattern generation at multiple sites

The level of LamB protein in the outer membrane of Escherichia coli was derepressed in the absence of a known inducer (maltodextrins) under carbohydrate-limiting conditions in chemostats. LamB protein contributed to the ability of the bacteria to remove sugar from glucose-limited chemostats, and well-characterized lamB mutants with reduced stability constants for glucose were less growth competitive under glucose limitation than those with wild-type affinity. In turn, wild-type bacteria were less growth competitive than lamB mutants with enhanced sugar affinity. In contrast to an earlier report, we found that LamB- bacteria were less able to compete in carbohydrate-limited chemostats (with glucose, lactose, arabinose, or glycerol as the carbon and energy sources) when mixed with LamB+ bacteria. The transport Km for [14C]glucose was affected by the presence or affinity of LamB, but only in chemostat-grown bacteria, with their elevated LamB levels. The pattern of expression of LamB and the advantage it confers for growth on low concentrations of carbohydrates are consistent with a wider role in sugar permeation than simply maltosaccharide transport, and hence the well-known maltoporin activity of LamB is but one facet of its role as the general glycoporin of E. coli. A corollary of these findings is that OmpF/OmpC porins, present at high levels in carbon-limited bacteria, do not provide sufficient permeability to sugars or even glycerol to support high growth rates at low concentrations. Hence, the sugar-binding site of LamB protein is an important contributor to the permeability of the outer membrane to carbohydrates in habitats with low extracellular nutrient concentrations.     

Role of the intermembrane-space domain of the preprotein receptor Tom22 in protein import into mitochondria

Tom22 is an essential component of the protein translocation complex (Tom complex) of the mitochondrial outer membrane. The N-terminal domain of Tom22 functions as a preprotein receptor in cooperation with Tom20. The role of the C-terminal domain of Tom22, which is exposed to the intermembrane space (IMS), in its own assembly into the Tom complex and in the import of other preproteins was investigated. The C-terminal domain of Tom22 is not essential for the targeting and assembly of this protein, as constructs lacking part or all of the IMS domain became imported into mitochondria and assembled into the Tom complex. Mutant strains of Neurospora expressing the truncated Tom22 proteins were generated by a novel procedure. These mutants displayed wild-type growth rates, in contrast to cells lacking Tom22, which are not viable. The import of proteins into the outer membrane and the IMS of isolated mutant mitochondria was not affected. Some but not all preproteins destined for the matrix and inner membrane were imported less efficiently. The reduced import was not due to impaired interaction of presequences with their specific binding site on the trans side of the outer membrane. Rather, the IMS domain of Tom22 appears to slightly enhance the efficiency of the transfer of these preproteins to the import machinery of the inner membrane.     

Multicopy suppressors of phenotypes resulting from the absence of yeast VDAC encode a VDAC-like protein

The permeability of the outer mitochondrial membrane to most metabolites is believed to be based in an outer membrane, channel-forming protein known as VDAC (voltage-dependent anion channel). Although multiple isoforms of VDAC have been identified in multicellular organisms, the yeast Saccharomyces cerevisiae has been thought to contain a single VDAC gene, designated POR1. However, cells missing the POR1 gene (delta por1) were able to grow on yeast media containing a nonfermentable carbon source (glycerol) but not on such media at elevated temperature (37 degrees C). If VDAC normally provides the pathway for metabolites to pass through the outer membrane, some other protein(s) must be able to partially substitute for that function. To identify proteins that could functionally substitute for POR1, we have screened a yeast genomic library for genes which, when overexpressed, can correct the growth defect of delta por1 yeast grown on glycerol at 37 degrees C. This screen identified a second yeast VDAC gene, POR2, encoding a protein (YVDAC2) with 49% amino acid sequence identity to the previously identified yeast VDAC protein (YVDAC1). YVDAC2 can functionally complement defects present in delta por1 strains only when it is overexpressed. Deletion of the POR2 gene alone had no detectable phenotype, while yeasts with deletions of both the POR1 and POR2 genes were viable and able to grow on glycerol at 30 degrees C, albeit more slowly than delta por1 single mutants. Like delta por1 single mutants, they could not grow on glycerol at 37 degrees C. Subcellular fractionation studies with antibodies which distinguish YVDAC1 and YVDAC2 indicate that YVDAC2 is normally present in the outer mitochondrial membrane. However, no YVDAC2 channels were detected electrophysiologically in reconstituted systems. Therefore, mitochondrial membranes made from wild-type cells, delta por1 cells, delta por1 delta por2 cells, and delta por1 cells overexpressing YVDAC2 were incorporated into liposomes and the permeability of resulting liposomes to nonelectrolytes of different sizes was determined. The results indicate that YVDAC2 does not confer any additional permeability to these liposomes, suggesting that it may not normally form a channel. In contrast, when the VDAC gene from Drosophila melanogaster was expressed in delta por1 yeast cells, VDAC-like channels could be detected in the mitochondria by both bilayer and liposome techniques, yet the cells failed to grow on glycerol at 37 degrees C. Thus, channel-forming activity does not seem to be either necessary or sufficient to restore growth on nonfermentable carbon sources, indicating that VDAC mediates cellular functions that do not depend on the ability to form channels.     

The 70 kDa subunit of replication protein A is required for the G1/S and intra-S DNA damage checkpoints in budding yeast

The rfa1-M2 and rfa1-M4 Saccharomyces cerevisiae mutants, which are altered in the 70 kDa subunit of replication protein A (RPA) and sensitive to UV and methyl methane sulfonate (MMS), have been analyzed for possible checkpoint defects. The G1/S and intra-S DNA damage checkpoints are defective in the rfa1-M2 mutant, since rfa1-M2 cells fail to properly delay cell cycle progression in response to UV irradiation in G1 and MMS treatment during S phase. Conversely, the G2/M DNA damage checkpoint and the S/M checkpoint are proficient in rfa1-M2 cells and all the checkpoints tested are functional in the rfa1-M4 mutant. Preventing S phase entry by alpha-factor treatment after UV irradiation in G1 does not change rfa1-M4 cell lethality, while it allows partial recovery of rfa1-M2 cell viability. Therefore, the hypersensitivity to UV and MMS treatments observed in the rfa1-M4 mutant might only be due to impairment of RPA function in DNA repair, while the rfa1-M2 mutation seems to affect both the DNA repair and checkpoint functions of Rpa70.     

Sydenham''s chorea

Many fungi undergo a morphological transition to filamentous growth in response to limiting nutrient conditions. Constitutively elongated Saccharomyces cerevisiae mutants (elm) have been isolated; the ELM1 gene encodes a putative serine/threonine protein kinase. A novel allele, elm1-15, has been isolated in an S288C-derived strain, which causes a pleiotropic phenotype, including media-specific growth effects, abnormal morphology and altered stress response, in cells that are auxotrophic for tryptophan. elm1-15 trp1 cells cannot use many nitrogen sources, are sensitive to amino acid analogues, have very low general amino acid permease activity and do not accumulate trehalose. In contrast, haploid elm1-15 TRP1 cells grow well in budding form on all media, are stress resistant and overaccumulate trehalose. Several lines of evidence suggest that Elm1 acts on functions related to the RAS/cAMP pathway. Overexpression of Elm1 partially rescues the ts phenotype of cdc25 and cyr1 mutants. Deletion of ELM1 in low PKA activity mutants increased the severity of their phenotypes, and activation of Ras2 decreases the cell elongation phenotype of elm1 mutants. A 'signal integration' model for the complex relationship of Elm1 and the RAS/cAMP pathway in controlling morphogenesis in response to nutrients is proposed.     

Role of the ninaC proteins in photoreceptor cell structure: ultrastructure of ninaC deletion mutants and binding to actin filaments

The ninaC proteins are found in Drosophila photoreceptor cells. Their primary sequences suggest they are kinase/myosin chimeras, but their myosin head-like domain is the most divergent amongst all the myosin-like proteins described to date. To investigate possible roles of the ninaC proteins in cell structure, we examined the ultrastructure of the photoreceptor cells in various ninaC mutants, and tested the ability of the proteins to interact with actin filaments in a myosin-like manner. In flies lacking the larger ninaC protein, p174, an ultrastructural phenotype was evident before eclosion. The axial actin cytoskeleton of the rhabdomeral microvilli appeared either fragmented or as an isolated structure, without linkage to the microvillar membrane. Deletion of the myosin head-like domain or the calmodulin-binding domain of p174 resulted in a similar abnormal cytoskeleton. Breakdown of the rhabdomeres followed, although at different rates depending on the deletion. Lack of the smaller protein, p132, per se did not result in photoreceptor degeneration, but in older flies there was an abnormal accumulation of multivesicular bodies. Moreover, the presence of p132 retarded the degeneration that occurs in the absence of p174, even though the p132 remained outside the rhabdomere. Biochemical studies showed that both ninaC proteins bind actin filaments and cosediment with actin filaments in an ATP-sensitive manner. These results outline structural roles for the ninaC proteins, and are consistent with the notion, suggested by their amino acid sequences, that the proteins are actin-based mechanoenzymes.     

Detection of quantitative trait loci in outbred populations with incomplete marker data

AcrA protein is a component of the multi-drug efflux complex AcrAB-TolC of Escherichia coli. Judged by the hypersusceptibility phenotype of acrA mutants, the AcrAB-TolC system pumps out an extraordinarily wide variety of antibiotics, chemotherapeutic agents, detergents and dyes. This complex traverses both the inner and outer membranes of E. coli and catalyzes efflux of the drugs directly into the medium. The coordinated operation of the inner membrane transporter AcrB and outer membrane channel TolC is thought to be mediated by AcrA. The latter is a lipoprotein located in the periplasmic space. We show here that a lipid-deficient derivative of AcrA is functionally active as demonstrated by the complementation of the hypersusceptibility phenotype of the acrA mutant. Purified non-lipidated and intact forms of AcrA were able to restore, with similar efficiency, the activity of AcrA-dependent efflux of erythromycin in Ca2+-sucrose-treated E. coli cells. Using analytical ultracentrifugation and dynamic light scattering techniques we determined hydrodynamic properties of the non-lipidated AcrA and found that AcrA exists in solution as a highly asymmetric monomeric molecule with an axial ratio of 8. This elongated shape of AcrA is compatible with the hypothesis that this protein spans the periplasmic space coordinating the concerted operation of inner and outer membrane components of the complex.     

Men as caregivers: reciprocal relationships or obligation?

The adult cuticular wing of Drosophila is covered by an array of distally pointing hairs that reveals the planar polarity of the wing. We report here that mutations in dachsous disrupt this regular pattern, and do so by affecting frizzled signaling. dachsous encodes a large membrane protein that contains many cadherin domains and dachsous mutations cause deformed body parts. We found that mutations in dachsous also result in a tissue polarity phenotype that at the cellular level is similar to frizzled, dishevelled and prickle, as many cells form a single hair of abnormal polarity. Although their cellular phenotype is similar to frizzled, dishevelled and prickle, dachsous mutant wings display a unique and distinctive abnormal hair polarity pattern including regions of reversed polarity. The development of this pattern requires the function of frizzled pathway genes suggesting that in a dachsous mutant the frizzled pathway is functioning - but in an abnormal way. Genetic experiments indicated that dachsous was not required for the intracellular transduction of the frizzled signal. However, we found that dachsous clones disrupted the polarity of neighboring wild-type cells suggesting the possibility that dachsous affected the intercellular signaling function of frizzled. Consistent with this hypothesis we found that frizzled clones in a dachsous mutant background displayed enhanced domineering non-autonomy, and that the anatomical direction of this domineering non-autonomy was altered in regions of dachsous wings that have abnormal hair polarity. The direction of this domineering nonautonomy was coincident with the direction of the abnormal hair polarity. We conclude that dachsous causes a tissue polarity phenotype because it alters the direction of frizzled signaling.     

Evaluation of fine needle capillary sampling in superficial and deep-seated lesions. An analysis of 670 cases

The gene rafY from the plasmid pRSD2, which enables Escherichia coli to grow on raffinose, was transferred into expression plasmid pUSL77. The protein was expressed in the porin-deficient Escherichia coli strain KS26 and was isolated and purified to homogeneity. The pure protein was reconstituted into lipid bilayer membranes. It formed an ion-permeable channel with a single-channel conductance of 2.9 nS of the open state in 1 M KCl, which is approximately twice of that of the general diffusion pores OmpF and OmpC of E. coli outer membrane. At lower pH the channel exhibited rapid flickering between three substates of the open channel. The RafY channel appears to be wide and water filled and has a small selectivity for cations over anions. Although RafY is part of an uptake and fermentation system for raffinose it does not contain a binding site for carbohydrates. Our results suggest that RafY is a general diffusion pore with a diameter, larger than that of the general diffusion porins OmpF and OmpC, that allows the diffusion of high-molecular-mass carbohydrates through the outer membrane.     

Functional interactions of genes mediating convergent extension, knypek and trilobite, during the partitioning of the eye primordium in zebrafish

Vertebrate eye development in the anterior region of the neural plate involves a series of inductive interactions dependent on the underlying prechordal plate and signals from the midline of the neural plate, including Hedgehog. The mechanisms controlling the spatiotemporal expression pattern of hedgehog genes are currently not understood. Cyclopia is observed in trilobite (tri) and knypek (kny) mutants with affected convergent extension of the embryonic axis during gastrulation. Here, we demonstrate that tri mutants show a high frequency of partial or complete cyclopia, kny mutants exhibit cyclopia infrequently, while knym119 trim209 double-mutant embryos have dramatically reduced convergent extension and are completely cyclopic. We analyzed the relationships between the convergent extension defect, the expression of hedgehog and prechordal plate genes, and the formation of cyclopia in knym119 and trim209 mutants. Our results correlate the cyclopia phenotype with the abnormal location of hh-expressing cells with respect to the optic primordium. We show that cyclopia in these mutants is not due to an incompetence of tri and kny cells to respond to Hedgehog signaling. Rather, it is a consequence of exceeding a critical distance (>40-50 micrometer) between hedgehog-expressing cells and the prospective eye field. We hypothesize that at this distance, midline cells are not in an appropriate position to physically separate the eye field and that HH and other signals do not reach the appropriate target cells. Furthermore, tri and kny have overlapping functions in establishing proper alignment of the anterior neural plate and midline cells expressing shh and twhh genes when the partitioning of the eye primordium takes place.     

Deletion of an amino-terminal sequence beta-catenin in vivo and promotes hyperphosporylation of the adenomatous polyposis coli tumor suppressor protein

Regulation of cell adhesion and cell signaling by beta-catenin occurs through a mechanism likely involving the targeted degradation of the protein. Deletional analysis was used to generate a beta-catenin refractory to rapid turnover and to examine its effects on complexes containing either cadherin or the adenomatous polyposis coli (APC) protein. The results show that amino-terminal deletion of beta-catenin results in a protein with increased stability that acts in a dominant fashion with respect to wild-type beta-catenin. Constitutive expression in AtT20 cells of a beta-catenin lacking 89 N-terminal amino acids (deltaN89beta-catenin) resulted in severely reduced levels of the more labile wild-type beta-catenin. The mutant beta-catenin was expressed at endogenous levels but displaced the vast majority of wild-type beta-catenin associated with N-cadherin. The deltaN89beta-catenin accumulated on the APC protein to a level 10-fold over that of wild-type beta-catenin and recruited a kinase into the APC complex. The kinase was highly active toward APC in vitro and promoted a sodium dodecyl sulfate gel band shift that was also evident for endogenous APC from cells expressing the mutant beta-catenin. Unlike wild-type beta-catenin, which partitions solely as part of a high-molecular-weight complex, the deltaN89 mutant protein also fractionated as a stable monomer, indicating that it had escaped the requirement to associate with other proteins. That similar N-terminal mutants of beta-catenin have been implicated in cellular transformation suggests that their abnormal association with APC may, in part, be responsible for this phenotype.     

SurA assists the folding of Escherichia coli outer membrane proteins

Many proteins require enzymatic assistance in order to achieve a functional conformation. One rate-limiting step in protein folding is the cis-trans isomerization of prolyl residues, a reaction catalyzed by prolyl isomerases. SurA, a periplasmic protein of Escherichia coli, has sequence similarity with the prolyl isomerase parvulin. We tested whether SurA was involved in folding periplasmic and outer membrane proteins by using trypsin sensitivity as an assay for protein conformation. We determined that the efficient folding of three outer membrane proteins (OmpA, OmpF, and LamB) requires SurA in vivo, while the folding of four periplasmic proteins was independent of SurA. We conclude that SurA assists in the folding of certain secreted proteins.     

Role of the negative charges in the cytosolic domain of TOM22 in the import of precursor proteins into mitochondria

TOM22 is an essential mitochondrial outer membrane protein required for the import of precursor proteins into the organelles. The amino-terminal 84 amino acids of TOM22 extend into the cytosol and include 19 negatively and 6 positively charged residues. This region of the protein is thought to interact with positively charged presequences on mitochondrial preproteins, presumably via electrostatic interactions. We constructed a series of mutant derivatives of TOM22 in which 2 to 15 of the negatively charged residues in the cytosolic domain were changed to their corresponding amido forms. The mutant constructs were transformed into a sheltered Neurospora crassa heterokaryon bearing a tom22::hygromycin R disruption in one nucleus. All constructs restored viability to the disruption-carrying nucleus and gave rise to homokaryotic strains containing mutant tom22 alleles. Isolated mitochondria from three representative mutant strains, including the mutant carrying 15 neutralized residues (strain 861), imported precursor proteins at efficiencies comparable to those for wild-type organelles. Precursor binding studies with mitochondrial outer membrane vesicles from several of the mutant strains, including strain 861, revealed only slight differences from binding to wild-type vesicles. Deletion mutants lacking portions of the negatively charged region of TOM22 can also restore viability to the disruption-containing nucleus, but mutants lacking the entire region cannot. Taken together, these data suggest that an abundance of negative charges in the cytosolic domain of TOM22 is not essential for the binding or import of mitochondrial precursor proteins; however, other features in the domain are required.     

NMR studies of the structure and stability of the 1 : 2 actinomycin D-d-pG-C complex in aqueous solution

Bacteriophage-resistant mutants isolated and classified in a previous study were examined for alterations in their lipopolysaccharide (LPS) composition, and properties likely to be affected by alterations in LPS composition were studied. It was found that many of the mutants of the Ktw (K2-resistance), Ttk (T2, T4, or K19 resistance), Bar (bacteriophage), Wrm (wide-range mutants), and miscellaneous resistance groups were altered in their response to a series of antibiotics and to two LPS-specific bacteriophages, C21 and U3. Furthermore, many of the bacteriophages to which these mutants were resistant adsorbed to LPS preparations. By direct sugar analysis of the mutant LPS preparations, it was shown that the mutants fitted into six distinct classes, which are readily derived from LPS core with a structure resembling that of Salmonella or Escherichia coli O100. A number of the mutants were shown to map between pyrE and mtl, which has been previously shown to be the site of a cluster of rfa genes in both Salmonella and E. coli. Outer membrane protein composition was studied in the above mutants using polyacrylamide gel electrophoresis. Some strains were shown to have alterations in the amount of major proteins. The nature of the bacteriophage receptors involved and the alterations leading to resistance are discussed.     

Functional analysis of vaccinia virus B5R protein: role of the cytoplasmic tail

Vaccinia extracellular enveloped virus (EEV) is important for cell-to-cell and long-range virus spread both in vitro and in vivo. Six genes have been identified that encode protein constituents of the EEV outer membrane, and some of these proteins are critical for EEV formation. The B5R gene encodes an EEV-specific type I membrane protein, and deletion of this gene markedly decreases EEV formation and results in a small plaque phenotype. Data suggest that the transmembrane domain, cytoplasmic tail, or both contain the EEV localization signals that are required for targeting of the B5R protein to EEV and for EEV formation. Here, we report the construction of mutant vaccinia viruses in which the wild-type B5R gene was replaced with a mutated one that encodes a protein with the putative cytoplasmic tail deleted. The mutated protein showed normal intracellular distribution and was properly incorporated into EEV. Vaccinia viruses expressing the B5R protein lacking the cytoplasmic tail formed plaques that were similar in type and size to those formed by wild-type viruses and produced equivalent amounts of infectious EEV. These results indicate that the B5R cytoplasmic tail is not necessary for EEV formation and points to the transmembrane domain as the major determinant for targeting the B5R protein to the outer membrane of EEV and for supporting EEV formation.     

A SecY homologue is required for the elaboration of the chloroplast thylakoid membrane and for normal chloroplast gene expression

Results of in vitro and genetic studies have provided evidence for four pathways by which proteins are targeted to the chloroplast thylakoid membrane. Although these pathways are initially engaged by distinct substrates and involve some distinct components, an unresolved issue has been whether multiple pathways converge on a common translocation pore in the membrane. A homologue of eubacterial SecY called cpSecY is localized to the thylakoid membrane. Since SecY is a component of a protein-translocating pore in bacteria, cpSecY likely plays an analogous role. To explore the role of cpSecY, we obtained maize mutants with transposon insertions in the corresponding gene. Null cpSecY mutants exhibit a severe loss of thylakoid membrane, differing in this regard from mutants lacking cpSecA. Therefore, cpSecY function is not limited to a translocation step downstream of cpSecA. The phenotype of cpSecY mutants is also much more pleiotropic than that of double mutants in which both the cpSecA- and DeltapH-dependent thylakoid-targeting pathways are disrupted. Therefore, cpSecY function is likely to extend beyond any role it might play in these targeting pathways. CpSecY mutants also exhibit a defect in chloroplast translation, revealing a link between chloroplast membrane biogenesis and chloroplast gene expression.     

The influence of poly-(L-lysine) and porin on the domain structure of mixed vesicles composed of lipopolysaccharide and phospholipid: an infrared spectroscopic study

Fourier transform infrared (FTIR) spectroscopy has been used to study the thermotropic phase behavior of binary lipid mixtures composed of deuterated phospholipids (PLs) and lipopolysaccharides (LPSs). Furthermore, the influence of an extrinsic high-molecular, polycationic polypeptide (poly-(L-lysine), PLL(500)) and an intrinsic membrane protein (outer membrane protein F, OmpF) on these binary mixtures was investigated by FTIR spectroscopy. "Deep rough" mutant LPS (ReLPS), isolated from Salmonella minnesota R595, and perdeuterated 1,2-dimyristoylphosphatidylethanolamine (DMPEd54) were used as model lipids. Deuteration of one of the lipids permitted the detection of lipid protein interaction with each lipid component separately. For this purpose, the symmetric >CH2 and >CD2 stretching bands were utilized as specific monitors to scrutinize the state of order of the membranes. From the individual phase transition temperatures Tm and the shape of the phase transition profiles, it is established that ReLPS and DMPEd54 are molecularly immiscible. In addition to the two domains of the pure lipid components, a third, domain-like structure is detected that may coexist with these pure domains. This domain-like structure undergoes a gel to liquid-crystalline L1 (beta <--> alpha) phase transition at temperatures distinctly different from that of the respective pure lipid domains. The nature of this type of domain is discussed in terms of a "border region" model that adequately explains the experimentally observed complex phase transition profiles. It is further demonstrated that the extrinsic polycationic polypeptide PLL(500) and the intrinsic, pore-forming protein OmpF isolated from Escherichia coli interact preferentially and highly specifically with the negatively charged ReLPS. Both the synthetic polypeptide and the pore-forming protein increased the tendency of ReLPS and DMPEd54 to segregate into distinct, well-separated domains. Whereas the transition profiles of the ternary system ReLPS/DMPEd54/PLL(500) showed the features of a phase segregation phenomenon not affecting the transition temperatures of the pure lipid components, the ternary system composed of ReLPS/DMPEd54 and OmpF exhibited phase transition curves that were characterized by an unspecific (DMPEd54/OmpF) and a strong and unique (ReLPS/OmpF) type of lipid-protein interaction. Furthermore, semiquantitative estimations supported the supposition that OmpF might be able to induce bilayer asymmetry in preformed symmetrical ReLPS/DMPEd54 vesicles.