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Biomedical subjects

R B Naso

Publications and source records attributed to R B Naso.

29 records · Page 2Linked to original sources
PubMed1976

A fucose-deficient glycoprotein precursor to Rauscher leukemia virus gp69/71.

Rauscher leukemia virus glycoprotein gp69/71 is synthesized in virus-infected cells by way of a 90,000 dalton glycoprotein precursor, termed Pr2a+b. This precursor could be labeled with radioactive glucosamine and methionine but not with fucose; whereas gp69/71 could be detected by labeling with radioactive glucosamine, fucose, or a mixture of amino acids but seemed to be deficient in methionine relative to Pr2a+b. Pr2a+b and gp69/71, were specifically precipitated by an antiserum prepared against phosphocellulose purified Rauscher gp69/71. Other virus-specific precursors, in addition to Pr2a+b, could be precipitated by antiserum prepared against detergent disrupted virus. Neither Pr2a+b nor gp69/71 was precipitated from cell extracts by antisera to Rauscher p30. Tryptic maps of Pr2a+b and gp69/71 showed that these glycoproteins share many tryptic peptides. Pulse-chase experiments with 14C-labeled amino acids indicated that gp69/71 was not radio-labeled during the pulse-labeling period but slowly appeared during the chase incubations. Pr2a+b, however, was rapidly labeled and tended to disappear during long chases. Furthermore, two nonglycosylated viral proteins, termed p15E and p12E, are structurally related to Pr2a+b. Viral p15E and p12E contained the same methionine-containing tryptic peptide fraction as Pr2a+b as determined by ion-exchange chromatography. These results provide evidence that Pr2a+b is a precursor to gp69/71 and establish a structural and possible precursor-product relationship between Pr2a+b, p15E, and p12E.

Amino Acid Sequence↗
PubMed1976

Selective decrease in the rate of cleavage of an intracellular precursor to Rauscher leukemia virus p30 by treatment of infected cells with actinomycin D.

The cleavage of an intracellular 67,000- to 70,000-dalton precursor, termed Pr4 to Rauscher leukemia virus (RLV) p30 protein proceeded at a slower rate when virus-producing cells were treated with actinomycin D (AMD). Treatment with AMD also caused a slight accumulation of Pr4 in purified early virus particles produced by a cell line which usually produces virions that contain little Pr4. The cleavage of other intracellular viral precursor polypeptides was not affected by treatment with AMD. Treatment of infected cells with cycloheximide, on the other hand, allowed the cleavage of Pr4 to proceed at the usual rate for a short period of time before further cleavage was drastically slowed or prevented. The cleavage of several other viral precursor polypeptides was also inhibited by treatment with cycloheximide. Different lines of evidence suggest that the mechanism of action of AMD is not due to a possible indirect effect on protein synthesis. Thus, the rate of cleavage of Pr4 was not affected by the length of pretreatment with AMD between 1 to 8 h. In addition, the combined effect of AMD and cycloheximide, at their maximal inhibitory concentrations, was greater than the effect of either drug alone, indicating the involvement of two at least partially different mechanisms in the action of AMD and cycloheximide. Furthermore, AMD did not affect the pulse labeling of viral precursor polypeptides. These results suggest that the interaction with viral RNA, whose production is inhibited by AMD, accelerates the cleavage of Pr4 to p30 during virus assembly. A hypothetical model is presented to illustrate th possible advantages of having a step in virus assembly in which genomic RNA interacts with a precursor to capsid proteins before the cleavage of that precursor.

Cell Line↗
PubMed1975

The cell-free translation of Rauscher leukemia virus RNA into high molecular weight polypeptides.

Rauscher leukemia virus (RLV) 65-S RNA, 35-S mengovirus RNA and reticulocyte A-rich RNA each stimulated cell-free protein synthesis in a JLS-V5 cell derived S-30 system. rRNA, however, was not stimulatory in this system. Of the stimulated protein products only those synthesized in response to added RLV RNA were immune-precipitable with anti-RLV rabbit serum. Furthermore, cell-free incubations with pactamycin at a concentration which specifically inhibits initiation and not elongation prevented the stimulation of amino acid incorporation in response to added RLV RNA. Analysis of the polypeptides synthesized by the cell-free system in response to reticulocyte A-rich RNA, showed them to be globin-like and, therefore, also mRNA specific. The RLV RNA-directed product included at least two classes of polypeptides (mol. wts of 140 000-185 000 and 50 000-75 000) both of which were larger than the group specific polypeptides of mature virions. None of the internal structural polypeptides of mature virions were synthesized in response to RLV RNA. The large molecular weight, viral-specific polypeptides are candidate precursor polyproteins which may represent the translational products of a polycistronic mRNA with a single initiation site.

Amino Acids↗
PubMed1975

Biosynthesis of Rauscher leukemia viral proteins.

Antisera to disrupted Rauscher leukemia virus (RLV) or to the purified Rauscher viral 30,000 dalton polypeptide were used to specifically precipitate newly snythetized intracellular viral polypeptides from extracts of infected NIH Swiss mouse cells (JLS-V16). Analysis by SDS-polyacrylamide gel electrophoresis (SDS-PHAGE) of extracts from cells pulse-labeled for 10-20 min with 35 S-methionine showed that immune precipitates contained none of the nonglycosylated internal structural polypeptides of mature viruses. The major viral-specific polypeptides labeled in 10 min included polypeptides of 180,000, 140,000, 110,000, 80,000, and 60,000 daltons with minor polypeptides of 65,000, 50,000, and 40,000 daltons. Labeling the intracellular virus-specific polypeptides with 14C-glucosamine indicated that the 180,000, 110,000, 80,000, and 60,000 dalton polypeptides were gylcosylated, and all but the 110,000 dalton polypeptides are contained in the mature virions. Based on pulse-chase experiments, it appears that at least 3 of the large polypeptides (140,000, 65,000, and 50,000 daltons) are precursors to the three major internal structural polypeptides of the mature virions.

Amino Acids↗
PubMed1975

Weight gain and heterosis at different stages of development of the rat.

Diallel crosses among four highly inbred lines of rats were made in order to evaluate their combining ability at 10 day intervals during postnatal growth. Analyses were undertaken to consider the relative magnitudes of different components of variation, including a heterotic effect, over a long developmental period. A general analysis of variance for least square means of body weights indicated that postnatal growth was influenced greatly by the maternal lines and to a lesser extent by the paternal line. Heterosis was measured as a statistically significant difference in body weight gain at 10 day intervals between the hybrid and either the averaged mean of the parent lines or the mean of the largest parent line. Of the effects analyzed, heterosis accounted for a major part of body weight variability in both sexes between 30 and 100 days of age but reached much higher levels in male than in female progeny. The heterotic response was most pronounced during the rapid growth phase; that is, between the ages of 20 to 50 days. Although interesting specific exceptions were observed, heterotic responses generally became more pronounced with increasing age through 100 days. Evidence for differential heterosis associated with particular lines was present in male progeny at growth stages immediately preceding and following the phase of most rapid growth. Specific combining ability, however, was generally lacking. Analyses of specific matings indicated that heterosis, in the lines tested, is a variable phenomenon which may be dependent upon the degree of genetic divergence between inbred parent lines and the combining ability of the genotype involved.

Age Factors↗