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Biomedical subjects

G S Martin

Publications and source records attributed to G S Martin.

119 records · Page 7Linked to original sources
PubMed1976

Cell-free translation of virion RNA from nondefective and transformation-defective Rous sarcoma viruses.

Nondefective and transformation-defective virion subunit RNAs from two strains of Rous sarcoma virus (RSV) were translated in cell-free systems derived from Krebs IIA ascites cells, wheat germ, and L-cells. In each case the predominant viral-specific product was a polypeptide of molecular weight 76,000 that is related to the internal viral group-specific antigens, as judged by immunoprecipitation with monospecific antisera and tryptic peptide fingerprinting. No difference could be detected between the translation products of 35S RNA from nondefective and transformation-defective RSV virions, nor of 35S RNA from different strains of RSV. The 76,000-molecular-weight polypeptide synthesized in response to 35S RNA in vitro was labeled with formyl-methionine from initiator tRNA. Models for viral protein synthesis are discussed in the light of these results, and arguments positioning the group-specific antigen gene at the 5' end of the 35S RNA are presented.

Antigens, Viral↗
PubMed1971

Temperature-dependent alterations in sugar transport in cells infected by a temperature-sensitive mutant of Rous sarcoma virus.

Cells transformed by Rous sarcoma virus take up 2-deoxyglucose at a faster rate than uninfected cells, under conditions where transformed and nontransformed cells grow at the same rate. In cells infected by a temperature-sensitive mutant, the stimulation of 2-deoxyglucose uptake is temperature dependent: the increase is observed at the permissive (36 degrees C), but not at the nonpermissive (41.5 degrees ) temperature. When infected cells are shifted from the nonpermissive temperature to the premissive temperature, the uptake of 2-deoxyglucose increases from a rate equal to that of uninfected cells to a rate equal to that of cells infected by the wild-type Schmidt-Ruppin Rous sarcoma virus. The reverse change occurs when the infected cells are shifted from the permissive to the nonpermissive temperature. By the use of cytosine arabinoside, an inhibitor of DNA synthesis, it was possible to show that DNA synthesis is neither required for the transformation, which occurs when the infected cells are shifted from the nonpermissive to the permissive temperature, nor for the phenotypic reversion, which occurs in the reverse shift.

Animals↗
PubMedDate not supplied

Phorbol ester and diacylglycerol induce protein phosphorylation at tyrosine.

The phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is an efficient tumour promoter in vivo. In vitro, TPA activates the phospholipid- and Ca2+-dependent protein kinase, kinase C. This activation is believed to reflect the structural similarity between TPA and diacylglycerol, the endogenous protein kinase C activator which is produced in vivo by hydrolysis of phosphatidylinositol (reviewed in ref. 3). Protein kinase C phosphorylates protein substrates at serine and threonine residues in vitro. The effects of TPA on cultured fibroblasts--including enhanced hexose uptake, disruption of actin stress fibres and growth stimulation--are very similar to those induced by certain retrovirus transforming proteins and by peptide growth factors such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and multiplication-stimulating activity (MSA). These transforming proteins and mitogenic agents seem to act by inducing tyrosine-specific protein phosphorylation. Such observations suggested that some of the effects of TPA in vivo may be mediated by protein phosphorylation at tyrosine residues. A 42,000-molecular weight (42 K) polypeptide was previously shown to be phosphorylated at tyrosine in cells transformed by avian sarcoma viruses and in cells stimulated by EGF, PDGF or MSA (J. Cooper, personal communication and refs 11 and 12; this polypeptide was originally designated 43 K or spot n in ref. 10). We show here that this polypeptide also becomes phosphorylated at tyrosine in cells treated with TPA. Furthermore, exogenously added diacylglycerol likewise stimulates the phosphorylation of this protein at tyrosine.

Animals↗
PubMedDate not supplied

Clonal response to ethanol of proliferating rat hepatoma cells in vitro.

We have grown HTC cells (ascites variant of Morris hepatoma 7288c) in spinner cultures in the presence of various concentrations of ethanol, both in short-term incubations and in chronically exposed cultures. In short-term exposures cell proliferation is decreased in a dose-related fashion, falling to approximately 25% of control values at 35 mM ethanol. In refed cultures maintained at ethanol concentrations gradually increased to 17 mM, there is an initial decrease in proliferation followed by stabilization. Comparison of the growth patterns of cells chronically exposed to ethanol with the growth patterns of uncloned naive cells suggests the presence of both ethanol-sensitive and -resistant HTC cell clones. Preliminary cloning experiments have been successful in demonstrating that HTC clones do exist which have widely varying responses to ethanol. Clones have been isolated which are growth-inhibited by low concentrations of ethanol whereas others are resistant or even stimulated in the same concentration range. The critical differences between ethanol-sensitive and -resistant HTC cells are currently unknown, but the general phenomenon of clonal selection during chronic ethanol exposure is of interest in the pathogenesis of alcohol-related diseases.

Adaptation, Physiological↗
PubMedDate not supplied

In vitro pullout strength of screws inserted in adult equine third metacarpal bone after overdrilling a 4.5-mm threaded insertion hole.

OBJECTIVE: To determine and compare the in vitro pullout strength of 5.5-mm cortical versus 6.5-mm cancellous bone screws inserted in the diaphysis and metaphysis of adult equine third metacarpal (MCIII) bones, in threaded 4.5-mm cortical bone screw insertion holes that were then overdrilled with a 4.5-mm drill bit to provide information relevant to the selection of a replacement screw if a 4.5-mm cortical screw is stripped. STUDY DESIGN: In vitro pullout tests of 5.5-mm cortical and 6.5-mm cancellous screws in equine MCIII bones. SAMPLE POPULATION: Two independent cadaver studies each consisting of 14 adult equine MCIII bones. METHODS: Two 4.5-mm cortical screws were placed either in the middiaphysis (study 1) or distal metaphysis (study 2) of MCIII bones. The holes were then overdrilled with a 4.5-mm drill bit and had either a 5.5-mm cortical or a 6.5-mm cancellous screw inserted; screw pullout tests were performed at a rate of 0.04 mm/second until screw or bone failure occurred. RESULTS: In diaphyseal bone, the screws failed in all tests. Tensile breaking strength for 5.5-mm cortical screws (997.5 +/- 49.3 kg) and 6.5-mm cancellous screws (931.6 +/- 19.5 kg) was not significantly different. In metaphyseal bone, the bone failed in all tests. The holding power for 6.5-mm cancellous screws (39.1 +/- 4.9 kg/mm) was significantly greater than 5.5-mm cortical screws (23.5 +/- 3.5 kg/mm) in the metaphysis. There was no difference in the tensile breaking strength of screws in the diaphysis between proximal and distal screw holes; however, the holding power was significantly greater in the distal, compared with the proximal, metaphyseal holes. CONCLUSIONS: Although tensile breaking strength was not different between 5.5-mm cortical and 6.5-mm cancellous screws in middiaphyseal cortical bone, holding power of 6.5-mm cancellous screws was greater than 5.5-mm cortical screws in metaphyseal bone of adult horses. CLINICAL RELEVANCE: If a 4.5-mm cortical bone screw strips in MCIII diaphyseal bone of adult horses, either a 5.5-mm cortical or 6.5-mm cancellous screw, however, would have equivalent pullout strengths. A 6.5-mm cancellous screw, however, would provide greater holding power than a 5.5-mm cortical screw in metaphyseal bone.

Animals↗