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Biomedical subjects

E C Murphy

Publications and source records attributed to E C Murphy.

At least 73 records · Page 4Linked to original sources
PubMed1983

P85: a gag-mos polyprotein encoded by ts110 Moloney murine sarcoma virus.

Antibody to a synthetic peptide (anti-C3 serum) with the predicted sequence of the C terminus of the Moloney murine sarcoma virus (strain 124) v-mos gene was used in immunoprecipitation experiments with cytoplasmic extracts of a clone of NRK cells infected with ts110 Moloney murine sarcoma virus, termed 6m2 cells. ts110 Moloney murine sarcoma virus codes for two viral proteins of 85,000 and 58,000 M(r), termed P85 and P58, respectively, in nonproducer 6m2 cells maintained at 33 degrees C. Anti-C3 serum specifically recognized [(3)H]leucine-labeled P85, but not P58, from infected cells maintained at 33 degrees C, whereas antiserum prepared against murine leukemia virus p12 recognized both proteins. Normal serum and anti-C3 serum pretreated with excess C3 peptide did not precipitate P85. Immunoprecipitation experiments after metabolic labeling of 6m2 cells with (32)P(i) showed that P85 is phosphorylated. Both anti-C3 and anti-p12 sera specifically detected (32)P-labeled P85. Cell-free translation of ts110 murine sarcoma virus/murine lukemia virus RNA produces P85, P58, and helper virus protein Pr63(gag). Anti-C3 serum specifically precipitated P85 but neither P58 nor Pr63(gag). We conclude from these studies that P85 is a product of both the gag and mos genes of ts110 murine sarcoma virus, and, therefore, it is referred to as P85(gag-mos). We have not detected any other v-mos gene product in ts110-infected cells.

Animals↗
PubMed1981

Facilitation of acetylcholine secretion at a mouse neuromuscular junction.

Facilitation of transmitter secretion from motor nerve terminals following one or more conditioning stimuli was examined in mouse sternomastoid muscles. Following a single conditioning stimulus at 20 degrees C, facilitation decayed exponentially during the first 70-80 msec with a time constant of 60 msec. After 70--80 msec, a small slower component of facilitation was apparent. Initial facilitation (obtained by extrapolation back to 'zero' time) had a value of approximately 0.5. Following more than one conditioning stimulus (2-6), initial facilitation was greater but the pattern of decay was similar, the slower component becoming more obvious as the number of conditioning stimuli was increased. The slow decay phase also appeared exponential. The pattern of decay of facilitation could be well fitted by the sum of two exponentials, F1 (0)exp(--t/tau 1) + F2(0)exp(--t/tau 2). After a single stimulus at 20 degrees C, tau 1 and tau 2 had mean values of 35 and 163 msec. The main effect of increasing the number of conditioning stimuli was to increase (F1(0) and F2(0) with little change in tau 1 or tau 2. Changing temperature from 30 degrees C to 10 degrees C increased F1(0) and tau 2 but had relatively little effect on F2(0) and tau 1.

Acetylcholine↗
PubMed1980

Characterization of viral polyproteins in cells transformed and producing Moloney murine sarcoma virus-124.

The viral proteins of Moloney murine sarcoma virus-transformed mouse cells (G8-124), that overproduce the sarcoma virus relative to helper leukemia virus, were examined by immunoprecipitation, sizing by gel electrophoresis and peptide mapping. Using antisera to the viral core proteins, a p10-deficient core polyprotein of 63 000 daltons (P63gag) was detected which was found to be a product of the MuSV-124 genome. Helper virus proteins Pr67gag, gPr85gag, Pr200gag-pol, and gPr83env were also detected and characterized. An unusual helper virus precursor polyprotein of 93 000 daltons was also detected and characterized. It was labeled with [3H]fucose, suggesting that it was an intermediate precursor containing gp70 on which further modification of the core oligosaccharide had occurred relative to gPr83env. The usual viral proteins were also found in sarcoma virus particles and they were undistinguishable in size from those of Moloney murine leukemia virus (cl-1 strain). These experiments together with pulse-labeling experiments performed in the presence of the arginine analog canavanine, which prevents proteolytic cleavage, suggest that the product derived from the Mo-MuSV-specific sequences must be expressed as a separate gene product since we were unable to detect in transformed cells a polyprotein containing both viral (e.g., 'gag', 'pol' or 'env') and non-viral components. Cell-free protein synthesis studies performed with Mo-MuSV-124 genomic RNA have confirmed this interpretation and have identified three size classes of polypeptides as translation products of the sarcoma virus genome. They are P63gag, P42-P38 and P23. Intracellular p63gag and cell-free synthesized P63gag, appear to have identical sizes, antigenic determinants and tryptic peptides. The P42-P38 proteins contain core protein determinants. P23 is not related to the products of the replication genes of MuLV. Thus, P23 is a candidate for the 'src' gene product of Mo-MuSV-124.

Animals↗
PubMed1980

Effect of canavanine on murine retrovirus polypeptide formation.

Canavanine is an arginine analog which is widely used to inhibit proteolytic processing of viral polyproteins. Certain results obtained with canavanine have suggested that it may have other effects. Therefore, we examined the effects of canavanine on the cell-free synthesis of murine retrovirus proteins. It was found that the electrophoretic mobility of the major gag-related cell-free product of both Rauscher murine leukemia virus (R-MuLV) and Moloney murine sarcoma virus 124 (Mo-MuSV-124) RNA was dependent on the concentration of canavanine used during translation. As the canavanine concentration was increased up to 4 mM, the apparent size of the major gag-related polypeptide also increased from 65,000 (R-MuLV RNA) or 63,000 (Mo-MuSV-124 RNA) to approximately 80,000 daltons. Additional increases in the canavanine concentration up to 12 mM did not increase the size of the gag gene product beyond 80,000 daltons. This change in electrophoretic mobility appeared to be due to a substitution of canavanine for arginine residues in the polypeptides, not to a change in their actual size. If amber suppressor tRNA and canavanine were used together during translation of Mo-MuSV-124 RNA and Mo-MuLV RNA, the results were also in agreement with this proposal. Translation experiments done with ovalbumin mRNA and mengovirus 35S RNA indicated that canavanine incorporation caused a shift in the electrophoretic mobility of ovalbumin from 43,000 to 45,000 daltons and caused the appearance of two slightly larger polypeptides in the 155,000- and 115,000- dalton regions of the mengovirus RNA cell-free product.

Animals↗
PubMed1980

Suppression of murine retrovirus polypeptide termination: effect of amber suppressor tRNA on the cell-free translation of Rauscher murine leukemia virus, Moloney murine leukemia virus, and Moloney murine sarcoma virus 124 RNA.

The effect of suppressor tRNA's on the cell-free translation of several leukemia and sarcoma virus RNAs was examined. Yeast amber suppressor tRNA (amber tRNA) enhanced the synthesis of the Rauscher murine leukemia virus and clone 1 Moloney murine leukemia virus Pr200(gag-pol) polypeptides by 10- to 45-fold, but at the same time depressed the synthesis of Rauscher murine leukemia virus Pr65(gag) and Moloney murine leukemia virus Pr63(gag). Under suppressor-minus conditions, Moloney murine leukemia virus Pr70(gag) was present as a closely spaced doublet. Amber tRNA stimulated the synthesis of the "upper" Moloney murine leukemia virus Pr70(gag) polypeptide. Yeast ochre suppressor tRNA appeared to be ineffective. Quantitative analyses of the kinetics of viral precursor polypeptide accumulation in the presence of amber tRNA showed that during linear protein synthesis, the increase in accumulated Moloney murine leukemia virus Pr200(gag-pol) coincided closely with the molar loss of Pr63(gag). Enhancement of Pr200(gag-pol) and Pr70(gag) by amber tRNA persisted in the presence of pactamycin, a drug which blocks the initiation of protein synthesis, thus arguing for the addition of amino acids to the C terminus of Pr63(gag) as the mechanism behind the amber tRNA effect. Moloney murine sarcoma virus 124 30S RNA was translated into four major polypeptides, Pr63(gag), P42, P38, and P23. In the presence of amber tRNA, a new polypeptide, Pr67(gag), appeared, whereas Pr63(gag) synthesis was decreased. Quantitative estimates indicated that for every 1 mol of Pr67(gag) which appeared, 1 mol of Pr63(gag) was lost.

Kinetics↗