The transforming protein of the MC29-related virus CMII is a nuclear DNA-binding protein whereas MH2 codes for a cytoplasmic RNA-DNA binding polyprotein.

Abstract

The acute avian leukemia viruses MH2 and CMII belong to the group of avian myelocytomatosis viruses, the prototype virus of which is MC29. This group of viruses is characterized by myc‐specific oncogenes which are presumably expressed as gag‐myc polyproteins. These polyproteins are synthesized in non‐producer cells transformed by MH2 and CMII and have mol. wts. of 100 000 (p100) and 90 000 (p90), respectively. Monoclonal antibodies against the N terminus of gag, p19, were used to localize the protein in MH2‐ and CMII‐transformed non‐producer fibroblasts. Immunofluorescence and cell fractionation indicated that greater than 90% of p100 from MH2 was located in the cytoplasm, whereas greater than 70% of p90 from CMII resided in the nucleus. Isolation of p100 and p90 by immunoaffinity chromatography resulted in an approximately 2000‐fold purification of the two polyproteins. Both of them, as well as p110 of MC29, bound to double‐stranded DNA of chick fibroblasts in vitro. However, only the MH2‐specific polyprotein p100 bound to RNA in vitro. Such a binding was not observed for p90 or p110, or for the purified gag precursor Pr76. Another polyprotein, gag‐erbA, from avian erythroblastosis virus, which is also located in the cytoplasm, did not bind to RNA. Our results indicate that the CMII‐specific polyprotein p90 behaved indistinguishably from the p110 of MC29. However, the MH2‐specific polyprotein p100 exhibited unique and novel properties which were distinct from a gag‐myc‐type protein.

myc and src oncogenes have complementary effects on cell proliferation and expression of specific extracellular matrix components in definitive chondroblasts.

“…Since the expression of myc alone in the MC29-and HB1-infected chondroblasts did not suppress the synthesis of the chondroblast-specific products, it is tempting to speculate that the observed suppression by MH2 is due to the action of mil. However, MH2 differs from MC29 and HB1 in that myc is expressed as a separate gene rather than as part of a gag fusion protein (4,18). It is possible that the presence of gag determinants in the protein modify its transforming effects, as has been reported for the transformation of hematopoietic cells by Abelson virus (24).…”

Induction of proliferation of neuroretina cells by long terminal repeat activation of the carboxy-terminal part of c-mil.

“…This cytoplasmic protein exhibits an in vitro serine-threonine kinase activity (4,20) and is responsible for avian embryo neuroretina (NR) cell proliferation in infected cultures (2). The v-mil gene represents a truncated form of the chicken cellular mil (c-mi!)…”

“…4 of the chicken c-mil sequences homologous to v-mil. This recombinant plasmid was constructed by changing a viral SmaI site into a XbaI site by linker insertion and then replacing the 2.5-kbp XbaI-HpaI gag-mil sequences by a 9.2-kbp XbaI-HpaI cellular mil fragment isolated from a clone of the chicken cellular locus (Fig.…”

c-Myc-Induced Genomic Instability

“…Avian leukosis virus-induced bursal lymphomas were first reported by Ellerman and Bang (1908). Subsequently, a series of avian retroviruses, including MH2, OK10, MH29, and CMII (Duesberg and Vogt 1979;Bister and Duesberg 1980), were isolated and found to contain MYC sequences (Chiswell et al 1981;Bunte et al 1983;Hann et al 1983;Kan et al 1983; Thompson et al 1987). The name MYC originated from "myelocytomatosis," which consists of avian leukosis (hematopoietic neoplasm) and sarcomas.…”