Dbp5p, a cytosolic RNA helicase, is required for poly(A)+ RNA export

The DBP5 gene encodes a putative RNA helicase of unknown function in the yeast Saccharomyces cerevisiae. It is shown here that Dbp5p is an ATP-dependent RNA helicase required for polyadenylated [poly(A)+] RNA export. Surprisingly, Dbp5p is present predominantly, if not exclusively, in the cytoplasm, and is highly enriched around the nuclear envelope. This observation raises the possibility that Dbp5p may play a role in unloading or remodeling messenger RNA particles (mRNPs) upon arrival in the cytoplasm and in coupling mRNP export and translation. The functions of Dbp5p are likely to be conserved, since its potential homologues can be found in a variety of eukaryotic cells.     

Saccharomyces cerevisiae Duo1p and Dam1p, novel proteins involved in mitotic spindle function

Recent evidence suggests that the cost as well as the morbidity associated with the maintenance of hemodialysis access is increasing rapidly; currently, the cost exceeds 1 billion dollars and access related hospitalization accounts for 25% of all hospital admissions in the U.S.A. This increase in cost and morbidity has been associated with several epidemiological trends that may contribute to access failure. These include late patient referral to nephrologists and surgeons, late planning of vascular access as well as a shift from A-V fistulaes to PTFE grafts and temporary catheters, which have a higher failure rate. The reasons for this shift in the types of access is multifactorial and is not explained by changes in the co-morbidities of patients presenting to dialysis. Surgical preference and training also appear to play an important role in the large regional variation and patency rate of these PTFE grafts. We propose a program for early placement of A-V fistulae, a continuous quality improvement, multidisciplinary program to monitor access outcome, the development of new biomaterials, and a research plan to investigate pharmacological intervention to reduce development of stenosis and clinical interventions to treat those that do develop, prior to thrombosis.     

NUP82 is an essential yeast nucleoporin required for poly(A)+ RNA export

We have isolated and characterized the gene encoding a novel essential nucleoporin of 82 kD, termed NUP82. Indirect immunofluorescence of cells containing an epitope tagged copy of the NUP82 localized it to the nuclear pore complex (NPC). Primary structure analysis indicates that the COOH-terminal 195 amino acids contain a putative coiled-coil domain. Deletion of the COOH-terminal 87 amino acids of this domain causes slower cell growth; deletion of the COOH-terminal 108 amino acids results in slower growth at 30 degrees C and lethality at 37 degrees C. Cells in which the last 108 amino acids of NUP82 have been deleted, when shifted to 37 degrees C, do not display any gross morphological defects in their nuclear pore complexes or nuclear envelopes. They do, however, accumulate poly(A)+ RNA in their nuclei at 37 degrees C. We propose that NUP82 acts as a linker to tether nucleoporins directly involved in nuclear transport to pore scaffolding via its coiled-coil domain.     

Interactions of p62(dok) with p210(bcr-abl) and Bcr-Abl-associated proteins

A 62-kDa Ras GTPase-activating protein (RasGAP)-associated protein is tyrosine-phosphorylated under a variety of circumstances including growth factor stimulation and in cells transformed by activated tyrosine kinases. A cDNA for p62(dok), reported to be the RasGAP-associated 62-kDa protein, was recently cloned from Abl-transformed cells. In this study, the interactions of p62(dok) with Bcr-Abl and associated proteins were examined. In 32D myeloid cells and Rat-1 fibroblasts transformed by p210(bcr-abl), p62(dok) is tyrosine-phosphorylated and co-immunoprecipitates with Bcr-Abl, RasGAP, and CrkL, a Src homology 2 (SH2) and SH3 domain-containing adaptor protein. Tyrosine-phosphorylated p62(dok) from cells expressing p210(bcr-abl) bound directly to the SH2 domains of Abl and CrkL in a gel overlay assay. Previous work has shown that an SH2 domain deletion mutant of Bcr-Abl is defective in transforming fibroblasts but remains capable of inducing myeloid growth factor independence. In both fibroblasts and myeloid cells expressing this mutant, p62(dok) is underphosphorylated as compared with cells expressing full-length p210(bcr-abl) but remains capable of associating with Bcr-Abl. However, in a gel overlay assay, p62(dok) from cells expressing the SH2 domain deletion was incapable of associating directly with SH2 domains of Abl and CrkL. Interestingly, no direct binding between Bcr-Abl and p62(dok) could be demonstrated in a yeast two-hybrid assay. These data suggest that indirect interactions mediate the interaction between Bcr-Abl and p62(dok) and that the SH2 domain of Bcr-Abl is required for hyperphosphorylation of p62(dok). Further, hyperphosphorylation of p62(dok) correlates with the ability of Bcr-Abl to transform fibroblasts but not with the induction of growth factor independence in myeloid cells.     

Pbp1p, a factor interacting with Saccharomyces cerevisiae poly(A)-binding protein, regulates polyadenylation

The poly(A) tail of an mRNA is believed to influence the initiation of translation, and the rate at which the poly(A) tail is removed is thought to determine how fast an mRNA is degraded. One key factor associated with this 3'-end structure is the poly(A)-binding protein (Pab1p) encoded by the PAB1 gene in Saccharomyces cerevisiae. In an effort to learn more about the functional role of this protein, we used a two-hybrid screen to determine the factor(s) with which it interacts. We identified five genes encoding factors that specifically interact with the carboxy terminus of Pab1p. Of a total of 44 specific clones identified, PBP1 (for Pab1p-binding protein) was isolated 38 times. Of the putative interacting genes examined, PBP1 promoted the highest level of resistance to 3-aminotriazole (>100 mM) in constructs in which HIS3 was used as a reporter. We determined that a fraction of Pbp1p cosediments with polysomes in sucrose gradients and that its distribution is very similar to that of Pab1p. Disruption of PBP1 showed that it is not essential for viability but can suppress the lethality associated with a PAB1 deletion. The suppression of pab1Delta by pbp1Delta appears to be different from that mediated by other pab1 suppressors, since disruption of PBP1 does not alter translation rates, affect accumulation of ribosomal subunits, change mRNA poly(A) tail lengths, or result in a defect in mRNA decay. Rather, Pbp1p appears to function in the nucleus to promote proper polyadenylation. In the absence of Pbp1p, 3' termini of pre-mRNAs are properly cleaved but lack full-length poly(A) tails. These effects suggest that Pbp1p may act to repress the ability of Pab1p to negatively regulate polyadenylation.     

Fast ion-exchange HPLC of proteins using porous poly(glycidyl methacrylate-co-ethylene dimethacrylate) monoliths grafted with poly(2-acrylamido-2-methyl-1-propanesulfonic acid)

Porous poly(glycidyl methacrylate-co-ethylene dimethacrylate) monoliths with different porous properties grafted with poly(2-acrylamido-2-methyl-1-propanesulfonic acid) chains using cerium(IV) initiated free-radical polymerization have been prepared and used for the separation of proteins in ion-exchange HPLC mode. Because of the presence of the large pores that are typical of monolithic separation media which allow easy flow of all of the mobile phase, the efficiency of the columns does not deteriorate even at high flow velocities as a result of the specific morphology of the monoliths. Optimization of the chromatographic conditions such as the shape of the mobile phase gradient and the flow rate allows for very fast separation of three proteins in less than 1.5 min.     

Polynucleotide phosphorylase is a component of a novel plant poly(A) polymerase

We have isolated cDNA clones encoding a novel RNA-binding protein that is a component of a multisubunit poly(A) polymerase from pea seedlings. The encoded protein bears a significant resemblance to polynucleotide phosphorylases (PNPases) from bacteria and chloroplasts. More significantly, this RNA-binding protein is able to degrade RNAs with the resultant production of nucleotide diphosphates, and it can add extended polyadenylate tracts to RNAs using ADP as a donor for adenylate moieties. These activities are characteristic of PNPase. Antibodies raised against the cloned protein simultaneously immunoprecipitate both poly(A) polymerase and PNPase activity. We conclude from these studies that PNPase is the RNA-binding cofactor for this poly(A) polymerase and is an integral player in the reaction catalyzed by this enzyme. The identification of this RNA-binding protein as PNPase, which is a chloroplast-localized enzyme known to be involved in mRNA 3'-end determination and turnover (Hayes, R., Kudla, J., Schuster, G., Gabay, L., Maliga, P., and Gruissem, W. (1996) EMBO J. 15, 1132-1141), raises interesting questions regarding the subcellular location of the poly(A) polymerase under study. We have reexamined this issue, and we find that this enzyme can be detected in chloroplast extracts. The involvement of PNPase in polyadenylation in vitro provides a biochemical rationale for the link between chloroplast RNA polyadenylation and RNA turnover which has been noted by others (Lisitsky, I., Klaff, P., and Schuster, G. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 13398-13403).     

A novel surgical glue composed of gelatin and N-hydroxysuccinimide activated poly(L-glutamic acid): Part 1. Synthesis of activated poly(L-glutamic acid) and its gelation with gelatin

Although fibrin glue has been widely used as a surgical adhesive, its components, fibrinogen and thrombin, obtained from human blood are not completely free from the risk of virus infection due to acquired immune deficiency and hepatitis. Recently, we have reported that a polymer pair composed of gelatin and poly(L-glutamic acid) (PLGA) promptly forms a gel and can firmly bond to soft tissues when crosslinked with the aid of water-soluble carbodiimide (WSC). The present study was undertaken to design a new PLGA-gelatin glue without using WSC. Two kinds of PLGA with molecular weights of 71 and 22 kDa were employed to prepare N-hydroxysuccinimide (NHS) activated derivatives. The NHS-activated PLGA could be synthesized at high yields and was found to be stable for an extended time without losing the ability to crosslink with gelatin when stored under a dry-cold condition. This NHS-activated PLGA could spontaneously form a gel with gelatin in an aqueous solution within a short time, comparable to a commercial fibrin glue, when gelation was allowed to proceed at pH 8.3. The NHS-activated PLGA prepared from PLGA with the molecular weight of 22 kDa could be readily dissolved at high concentrations and its ability to form a gel was maintained for more than 10 min when an acidic 8% NHS-activated PLGA solution was used. The bonding strength of PLGA gelatin glues with natural tissue was higher than that of fibrin glue. These findings strongly suggest that this combination of gelatin and NHS-PLGA is very promising as a surgical adhesive and may possibly replace fibrin glues prepared from human blood components.     

Ribosomal association of poly(A)-binding protein in poly(A)-deficient Saccharomyces cerevisiae

Poly(A)-binding protein, the most abundant eukaryotic mRNP protein, is known primarily for its association with polyadenylate tails of mRNA. In the yeast, Saccharomyces cerevisiae, this protein (Pabp) was found to be essential for viability and has been implicated in models featuring roles in mRNA stability and as an enhancer of translation initiation. Although the mechanism of action is unknown, it is thought to require an activity to bind poly(A) tails and an additional capacity for an interaction with 60 S ribosomal subunits, perhaps via ribosomal protein L46 (Rpl46). We have found that a significant amount of Pabp in wild-type cells is not associated with polyribosome complexes. The remaining majority, which is found in these complexes, maintains its association even in yeast cells deficient in polyadenylated mRNA and/or Rpl46. These observations suggest that Pabp may not require interaction with poly(A) tails during translation. Further treatment of polyribosome lysates with agents known to differentially disrupt components of polyribosomes indicated that Pabp may require contact with some RNA component of the polyribosome, which could be either non-poly(A)-rich sequences of the translated mRNA or possibly a component of the ribosome. These findings suggest that Pabp may possess the ability to bind to ribosomes independently of its interaction with poly(A). We discuss these conclusions with respect to current models suggesting a multifunctional binding capacity of Pabp.     

Specific binding to a novel and essential Golgi membrane protein (Yip1p) functionally links the transport GTPases Ypt1p and Ypt31p

The regulation of vesicular transport in eukaryotic cells involves Ras-like GTPases of the Ypt/Rab family. Studies in yeast and mammalian cells indicate that individual family members act in vesicle docking/fusion to specific target membranes. Using the two-hybrid system, we have now identified a 248 amino acid, integral membrane protein, termed Yip1, that specifically binds to the transport GTPases Ypt1p and Ypt31p. Evidence for physical interaction of these GTPases with Yip1p was also demonstrated by affinity chromatography and/or co-immunoprecipitation. Like the two GTPases, Yip1p is essential for yeast cell viability and, according to subcellular fractionation and indirect immunofluorescence, is located to Golgi membranes at steady state. Mutant cells depleted of Yip1p and conditionally lethal yip1 mutants at the non-permissive temperature massively accumulate endoplasmic reticulum membranes and display aberrations in protein secretion and glycosylation of secreted invertase. The results suggests for a role for Yip1p in recruiting the two GTPases to Golgi target membranes in preparation for fusion.     

Selected nuclear matrix proteins are targets for poly(ADP-ribose)-binding

Recent evidence suggests that poly(ADP-ribose) may take part in DNA strand break signalling due to its ability to interact with and affect the function of specific target proteins. Using a poly(ADP-ribose) blot assay, we have found that several nuclear matrix proteins from human and murine cells bind ADP-ribose polymers with high affinity. The binding was observed regardless of the procedure used to isolate nuclear matrices, and it proved resistant to high salt concentrations. In murine lymphoma LY-cell cultures, the spontaneous appearance of radiosensitive LY-S sublines was associated with a loss of poly(ADP-ribose)-binding of several nuclear matrix proteins. Because of the importance of the nuclear matrix in DNA processing reactions, the targeting of matrix proteins could be an important aspect of DNA damage signalling via the poly ADP-ribosylation system.     

Familial partial duplication (1)(p21p31)

A consecutive series of 117 patients treated for hip fracture were followed up prospectively for three years. The mortality was highest during the first year. The proportion living in nursing-homes was increased by 50% at one year and 25% at three years compared with before injury, but the absolute numbers were reduced because of mortality. Reduced pre-injury mobility greatly increased the risk of becoming institutionalized. The proportion of the survivors who walked without aids was reduced by more than half at one and three years. The proportion of those bedridden increased six fold. Among patients who walked without aids before fracture 31% needed two sticks or more and 7% were bedridden after one year. Among those who before fracture walked with one stick or more, the percentages were 91 and 43.