Light promotion of hypocotyl gravitropism of a starch-deficient tobacco mutant correlates with plastid enlargement and sedimentation

Dark-grown hypocotyls of a starch-deficient mutant (NS458) of tobacco (Nicotiana sylvestris) lack amyloplasts and plastid sedimentation, and have severely reduced gravitropism. However, gravitropism improved dramatically when NS458 seedlings were grown in the light. To determine the extent of this improvement and whether mutant hypocotyls contain sedimented amyloplasts, gravitropic sensitivity (induction time and intermittent stimulation) and plastid size and position in the endodermis were measured in seedlings grown for 8 d in the light. Light-grown NS458 hypocotyls were gravitropic but were less sensitive than the wild type (WT). Starch occupied 10% of the volume of NS458 plastids grown in both the light and the dark, whereas WT plastids were essentially filled with starch in both treatments. Light increased plastid size twice as much in the mutant as in the WT. Plastids in light-grown NS458 were sedimented, presumably because of their larger size and greater total starch content. The induction by light of plastid sedimentation in NS458 provides new evidence for the role of plastid mass and sedimentation in stem gravitropic sensing. Because the mutant is not as sensitive as the WT, NS458 plastids may not have sufficient mass to provide full gravitropic sensitivity.     

Staphylococcus aureus nasal colonization in HIV-seropositive and HIV-seronegative drug users

Five cases of adenoid basal carcinoma (ABC) of the uterine cervix were examined for the presence of p53 tumor suppressor gene, K-ras-2 oncogene, and human papillomavirus (HPV). A topographic genotyping approach was used to search for point mutations in K-ras-2 (exon 1 and 2) and p53 (exons 5 to 8) in archival formalin-fixed tissue blocks. Minute target sites were selected from polymerase chain reaction (PCR) amplified and directly sequenced tissue sections. Tissue sections were additionally subjected to immunohistochemical staining for p53 and WAF-1 protein. Because wild type p53 induces WAF-1 gene expression, immunohistochemical staining for WAF-1 protein using monoclonal antibodies may serve as an indirect means to test for p53 mutational damage. Mutational genotype was compared to histopathologic features and immunohistochemical staining. To study the role of HPV, L1 region consensus primers were used to amplify topographic samples, followed by HPV genotyping by direct sequencing and comparison to known viral strains. ABC was found to contain HPV in all cases, proven by genotyping to be HPV type 16 in each case. The virus showed no evidence of genomic variation from prototype HPV type 16 in the L1 segment examined. No K-ras-2 point mutations were identified. p53 immunopositivity was present in all tumors, being weak and focal in 4 and strong and diffuse in 1. WAF-1 immunostaining was positive in two tumors showing weak focal p53 immunopositivity. The single strong and diffuse p53 immunopositive tumor was negative for WAF-1 and was shown to contain a missense p53 point mutation (exon 7-codon 248 tryptophan). In conclusion, ABC is characterized by the presence of HPV type 16. K-ras-2 point mutation appears to play no role in the development of this tumor. p53 gene alterations are common including wild type hyperexpression (weak focal p53 immunopositivity, WAF-1 positivity, no mutational change) and p53 point mutational damage.     

Photodimers of 9-Haloanthracenes as Initiators in Atom Transfer Radical Polymerization: Effect of the Bridgehead Halogen

Summary Photodimers of 9-chloroanthracene, formed by a [4+4] cycloaddition reaction of 9-chloroanthracene, were used as initiators in the atom transfer radical polymerization of styrene and compared to results previously obtained using photodimers of 9-bromoanthracene as the initiator. Heat-induced cleavage of the photodimer coupled with slow initiation from the bridgehead radical have been used to account for the lack of control in the systems, and thus changing the halogen on the initiating photodimer could support or refute this model. Reactions performed using analogous procedures produced polymers with number average molecular weight (M_n) values significantly higher in the case of 9-chloroanthracene photodimer-initiated systems, with similar polydispersity index (PDI) values observed in trials catalyzed with CuCl or CuBr. Polymer products showed absorbance bands indicative of regenerated anthracene in all cases, consistent with heat-induced cleavage of the photodimer during the course of the polymerization. Kinetic plots demonstrated that the polymerizations initiated with photodimers of 9-chloroanthracene showed maximum M_n values were obtained after approximately 10% monomer conversion, with a decline in M_n as a function of monomer conversion after this point. The data support slower initiation in the case of 9-chloroanthracene photodimers, followed by heat-induced cleavage throughout the polymerization system.     

Allogeneic vascularized transplantation of human femoral diaphyses and total knee joints--first clinical experiences

This article has presented the preliminary results of three patients who received vascularized allogeneic femoral diaphyses and three patients having undergone vascularized transplantation of fresh and perfused total human knee joints. The large osseous defects in the femora followed osteomyelitis and chondrosarcoma. The three knee joints were lost due to various trauma mechanisms. All grafts were harvested within 25 hours from multiorgan donors perfused with 4 L of UW solution. All osteosyntheses were performed employing intramedullary nails. Vascular pedicles of the grafts were anastomosed end-to-side to the superficial femoral artery and vein in the adductorial canal of the recipient thigh. Immunosuppression was based mainly on two drugs: CyA and AZA. Perfusion of the grafts was demonstrated by DSA, and bone metabolism in the graft by SPECT scintigraphy. Six months after the operation all osteotomies demonstrated callus formation and osseous consolidation in conventional radiographs. Biopsies of the grafted bone revealed intact osteocytes, and arthroscopy of the transplanted knee joints demonstrated intact synovial, chondral, and ligamentous structures. From the surgical aspect, the vascularized transplantation of the femoral diaphyses and total knee joints is technically feasible. The main problems are immunologic. All transplantations were performed with respect to ABO compatibility, but with a large HLA mismatch. Therefore, acute and chronic rejection crises were observed. In total synovial joints, lifelong immunosuppression of graft recipients seems to be currently unavoidable.     

Rabbit beta-globin is extended beyond its UGA stop codon by multiple suppressions and translational reading gaps

Translational reading gaps occur when genetic information encoded in mRNA is not translated during the normal course of protein synthesis. This phenomenon has been observed thus far only in prokaryotes and is a mechanism for extending the reading frame by circumventing the normal stop codon. Reading frames of proteins may also be extended by suppression of the stop codon mediated by a suppressor tRNA. The rabbit beta-globin read-through protein, the only known, naturally occurring read-through protein in eukaryotes, was sequenced by ion trap mass spectrometry to determine how the reading frame is extended. Seven different proteolytic peptide fragments decoded by the same sequence that spans the UGA stop codon of rabbit beta-globin mRNA were detected. Three of these peptides contain translational reading gaps of one to three amino acids that correspond to the UGA stop codon site and/or one or two of the immediate downstream codons. To our knowledge, this is the first reported example of the occurrence of reading gaps in protein synthesis in eukaryotes. This event is unique in that it is associated with bypasses involving staggered lengths of untranslated information. Four of the seven peptides contain serine, tryptophan, cysteine, and arginine decoded by UGA and thus arise by suppression. Serine is donated by selenocysteine tRNA, and it, like the other tRNAs, has previously been shown to suppress UGA in vitro in mammals, but not in vivo.     

The effects of Escherichia coli STa (heat stable) toxin on the contractility of isolated human myometrium in vitro

OBJECTIVE: The purpose of the study was to assess the effects of Escherichia coli STa (heat stable) toxin on isolated human myometrial response to oxytocin. METHODS: One hundred and sixteen muscle strips were obtained from the lower uterine segment of 42 women undergoing cesarean section at term. Amniotic membranes and decidua were excluded. Uterine contractility in response to cumulative doses of E. coli STa toxin was recorded, as well as uterine response to cumulative doses of oxytocin before and after incubation with STa toxin or vehicle. The 50th percentile effective oxytocin concentration (EC50) of muscle strips with and without spontaneous activity before and after the incubation with STa toxin or vehicle was calculated. A paired t test was used for comparison. RESULTS: Muscle strips with and without spontaneous activity responded to cumulative doses of oxytocin before and after the incubation with STa toxin or vehicle. No differences in contraction force, duration, or frequency were noted between the groups (P > 0.05). Furthermore, this toxin was not able to induce uterine contractility when tested alone. CONCLUSIONS: The inability of this toxin to affect myometrial response to oxytocin in this study may be due to the absence of amnion cells, chorion, or decidua. Other possible explanations for the lack of response are discussed.     

Human endothelial cell storage granules: a novel intracellular site for isoforms of the endothelin-converting enzyme

The participation of oxidative mechanisms in major histocompatibility complex (MHC) class II-restricted antigen presentation was studied in vitro. In general, antigen processing is inhibited when peritoneal macrophages (MO) are incubated with scavengers of reactive oxygen intermediates (ROI): mannitol (an.OH scavenger), dimethylurea (DMTU, which reacts with H2O2 and HOCl) and NCO-700 (an epoxysuccinic acid derivative which inhibits oxidant production by activated phagocytes and can scavenge reactive oxygen species in both NaOCl and hypoxanthine (XOD) systems). However, neither rotenone and antimycins (inhibitors of O-2 production at the NADH dehydrogenase and ubiquinone-cytochrome b regions, respectively) nor aminoguanidine (an inducible nitric oxide synthase inhibitor) impaired antigen presentation, thus indirectly discarding the participation of mitochondrial oxidation and reactive nitrogen intermediates (RNI) in antigen processing. ROI scavengers do not inhibit the MHC class II-restricted presentation of antigens that need processing but have their disulphide bonds reduced. It can be shown that oxidation of protein antigens (either by chlorination or performic acid treatment) allow protein unfolding and enhance both processing and exposure of immunogenic epitopes to specific T cells.