Common precursor for Rauscher leukemia virus gp69/71, p15(E), and p12(E).

Rauscher murine leukemia virus glycoprotein gp69/71 and non-glycosylated p15(E) are synthesized by way of a 90,000-dalton precursor glycoprotein, termed Pr2a+b. Peptide mapping experiments showed that Pr2a+b contains all the tyrosine-containing tryptic peptides of gp69/71. Two additional tyrosine-containing tryptic peptides in Pr2a+b that are not detected in gp69/71 are found in p15(E). Thus, gp69/71 and p15(E) peptide sequences account for all the tyrosine tryptic peptides of Pr2a+b. The gene order of the two proteins was determined by pulse-labeling infected cells in the presence and absence of pactamycin at concentrations of the inhibitor that prevent initiation of translation, but not elongation. The gene order was found to be: (2)HN-gp69/71-p15(E)-COOH. A newly identified major viral protein, termed p12(E), migrates in sodium dodecyl sulfate-polyacrylamide gels in the "p12" region. It is related to p15(E) as determined by tryptic mapping experiments. p15(E) and p12(E) are not phosphorylated, and both can be separated from phosphoprotein p12 by guanidine hydrochloride-agarose chromatography. p12(E) and p15(E) elute in the void volume fraction, whereas phosphoprotein p12 elutes between p15 and p10. The two p12 proteins can also be separated from each other by two-dimensional gel electrophoresis involving isoelectric focusing in the first dimension and sodium dodecyl sulfate-gel electrophoresis in the second dimension.

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.

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.

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.

Identification of the forms of vitamin B 6 present in the culture media of "vitamin B 6 control" mutants.

An Escherichia coli mutant resistant to isoniazid (WG497) contained 0.6 mumole of extracellular pyridoxamine and pyridoxamine phosphate in the early stationary phase. A suppressed lysine mutant (AT1024) contained 1.4 mumoles of pyridoxal phosphate under the same conditions. The internal concentration of vitamin B(6) was one-half of normal for AT1024 and increased fivefold for WG497.