Comparative tryptic peptide mapping studies suggest a role in cell transformation for the gag-related protein of avian erythroblastosis virus and avian myelocytomatosis virus strains CMII and MC29.

Abstract

The gag-related proteins found in cells transformed by avian erythroblastosis virus (AEV) and the avian myelocytomatosis viruses MC29 and CMII have been compared by tryptic peptide fingerprinting. A comparison of the methionine-containing tryptic peptides of the AEV 75-kilodalton protein, the CMII 90-kilodalton protein, and the MC29 110-kilodalton protein with the gag gene product Pr76 of their naturally occurring helper leukemia viruses enabled us to distinguish those peptides related to the gag gene from the non-gag-related peptides. The 12 non-gag peptides found in the AEV 75-kilodalton protein were unique to this protein and not found in the MC29 110-kilodalton or CMII 90-kilodalton proteins. In contrast, the MC29 110-kilodalton protein shared two methionine-containing non-gag tryptic peptides with the CMII 90-kilodalton protein. When these experiments were repeated with ['4C]lysine and [14C]arginine as the labeled amino acids, the MC29 Il1-kilodalton protein and the CMII 90-kilodalton protein were found to share 30 out of approximately 40 non-gag-related peptides. These results demonstrate that viruses with a similar transformation spectrum synthesize related proteins and suggest that the gag-related proteins represent the transforming proteins of the replication-defective avian leukemia viruses. Avian leukemia viruses can be divided into two groups: (i) the nondefective avian leukemia viruses (ALVs) which predominantly induce lymphatic leukemia after long periods of latency, and (ii) the replication-defective acute leukemia viruses (DLVs), which cause acute erythroid and myeloid leukemias in addition to other nonhematopoietic neoplasms after short periods of latency (for review, see ref. 1). The DLVs have been subdivided into three classes on the basis of their in vivo and in vitro transforming potential. These are (i) avian erythroblastosis virus (AEV)-type strains (for example, strains R and ES4), (ii) avian myeloblastosis virus-type strains (for example, E26), and (iii) avian myelocytomastosis virus (MC29)-type strains (for example, CMII, OK-10, and MH-2) (1, 2).The genome of ALV consists of three genes that code for the structural proteins of the virus. Analysis of cells infected with such nondefective viruses reveals the presence of three precursor polyproteins: Pr76, the product of the gag gene (3, 4); gPr95, the product of the env gene (5-8); and Prl80, the putative reverse transcriptase precursor (7, 9). On the other hand, analysis of nonproducer cells transformed by DLVs has shown that they contain none of these standard precursor proteins. Instead, they have been found to contain proteins related to, but distinct from, the gag gene product of the ALVs. For example, cells transformed by strains R and ES4 of AEV were shown to contain a 75-kilodalton protein (AEV-75), which was related to the gag gene product by virtue of containing the sequences present in the p19 protein, but the additional 50-60 kilodaltons of protein was shown to be unrelated to the viral The publication costs of this ar...

Isolation and biochemical characterization of partially transformation-defective mutants of avian myelocytomatosis virus strain MC29: localization of the mutation to the myc domain of the 110,000-dalton gag-myc polyprotein

“…We analyzed further the relationship of 100K, 95K, and 90K were very similar and showed no apparent loss of gag or MC29-specific peptides (unpublished data), suggesting that the alterations which had occurred were in regions of the proteins which did not contain any methionine tryptic peptides. Figure 4 shows the two-dimensional tryptic peptide maps of MC29 110K, Pr76, 10A 100K, 10G 95K, and 10H 90K, plus a schematic representation showing the assignments of the gagand myc-specific peptides in the 110K protein, as determined previously (20), and the changes which occurred in 100K, 95K, and 90K. A comparison of the tryptic peptide maps of MC29 110K and MC29-AV Pr76 (Fig.…”

“…It is thought that this RNA species encodes the 110,000-dalton (110K) gag-related polyprotein which is detected in all MC29-transformed cells (3,7,23). The 110K polyprotein has been shown by tryptic peptide analysis to be a hybrid protein containing at the amino terminus gag sequences encoded by the Agag gene and at the carboxy terminus MC29specific sequences, which are presumed to be encoded by the v-myc sequence (20,28). The findings that the 110K polyprotein was partially encoded by v-myc and that it was the only virusspecific protein detected in MC29-transformed nonproducer cells supported the hypothesis that the 110K protein is involved in transformation (3,11,15,23,28).…”

The avian erythroblastosis virus erbA oncogene encodes a DNA-binding protein exhibiting distinct nuclear and cytoplasmic subcellular localizations

“…The avian erythroblastosis virus (AEV) possesses two distinct loci that mediate oncogenic transformation by this retrovirus, v-erbA and v-erbB (2,27,30,32,38,39,43,51,58). The v-erbB gene is both necessary and sufficient for oncogenesis and encodes a tyrosine-specific protein kinase (17,20,26,31,41,50,57).…”

Deletions Within the Transformation-Specific RNA Sequences of Acute Leukemia Virus MC29 Give Rise to Partially Transformation-Defective Mutants

“…The only viral protein product which is found in cells transformed by MC29 in the absence of helper virus (nonproducer cells) is a 110-kilodalton phosphorylated polyprotein (p110) that is antigenically related to the gag gene (4,5). In vitro translation and peptide mapping have shown that this protein is coded for by Agag and the MC29-specific RNA sequence (19,22,27). Hence, it appeared that the genetic unit Agag-myc is the onc gene of MC29 and that plO is the transforming protein.…”