Glycoprotein encoded by the Friend spleen focus-forming virus

Abstract

The Friend spleen focus-forming virus (F-SFFV) released from cultured erythroleukemia cells (cell line F4-6/K) was cloned free of its helper lymphatic leukemia virus (F-MuLV). After allowing adsorption to Sc-1 fibroblasts at a low multiplicity of infection, the cells were seeded individually into wells of a microtiter test plate and the resulting colonies were grown into large cultures. Among 14 of these cell cultures that have been analyzed thoroughly, 6 contained F-SFFV alone, 1 contained F-MuLV plus F-SFFV, and 7 were uninfected. Each of the Sc-1 cell lines which had been infected with cloned F-SFFV contained a glycoprotein with an apparent molecular weight of 55,000 (gp55) that was absent from the cell lines that lacked F-SFFV. gp55 was also present in Friend erythroleukemia cells and in fibroblasts infected with an F-SFFV that had been doubly cloned in another laboratory. These results indicate that gp55 is encoded by the F-SFFV genome. gp55 has the following additional properties. It can be immunoprecipitated with antiserum made to the F-MuLV virion envelope glycoprotein (gp75). Its unglycosylated polypeptide, formed in cells treated with 2-deoxy-D-glucose, has a molecular weight of approximately 45,000. Its tryptic peptide map contains peptides in common with F-MuLV gp75 but it also contains unique peptides. It appears to be absent or present in only low concentrations in erythroleukemia cell plasma membranes as determined by lactoperoxidase-catalyzed iodination, and it accumulates intracellularly in large amounts. In addition, it is absent from released virions. The majority of the cellular gp55 has an isoelectric point of 8.5 to 9.0. These results are consistent with the idea that an env gene recombination event was involved in the origin of F-SFFV.

Erythroleukemia induction by replication-competent type C viruses cloned from the anemia- and polycythemia-inducing isolates of Friend leukemia virus.

“…The SFFVp genome has been shown to include specific sequences that are not shared with its helper, F-MuLVI, (7,19,20). In addition, as shown previously (21,22) and in the accompanying study (1), both SFFV isolates encode a 55,000-mol wt protein related to the env gene product of murine xenotropic leukemia viruses, whereas Friend MuLV does not. Given the biological and molecular properties of the related Friend virus isolates, it will be of interest to determine whether the erythroleukemias associated with each of these viruses develop as the result of common or distinct molecular mechanisms.…”

trans-dominant interference with virus infection at two different stages by a mutant envelope protein of Friend murine leukemia virus

“…Cells and viruses. 745a is a Friend murine erythroleukemia cell line, which harbors FMLV and spleen focus-forming virus (SFFV) (6,25). FR-6 is an immunoselected mutant cell line which survived the complement-dependent cytotoxicity caused by an anti-ecotropic MLV antiserum, anti-FN2 (a-FN2) (38).…”

Modification of simian virus 40 large tumor antigen by glycosylation

“…Glycosylation of viral transformation proteins has been recognized in only a few retrovirus systems and has not previously been conclusively demonstrated with any DNA tumor virus. All of the known retroviral transformation glycoproteins are N-glycosylated (Dresler et aL, 1979;Hayman et aL, 1983;Privalsky et cd, 1983); none has been shown to be Oglycosylated. Only a single viral glycoprotein, the El matrix glycoprotein of certain coronaviruses, is believed to be exclusively 0-glycosylated (Holmes et d, 1981;Niemann and Klenk, 1981).…”