A cell-determined deficiency in the processing of gag proteins of murine leukemia virus 334C

The effect of cerulenin on the synthesis of the precursor gag polyprotein in defective murine leukemia and sarcoma virus producing cell lines

The effect of cerulenin, an inhibitor of de novo fatty acid (and cholesterol) biosynthesis, on the synthesis of the precursor gag polyprotein, Pr65gag in a defective murine leukemia virus (334C) producing murine cell line (3JE) and a defective murine sarcoma virus (Gazdar) producing hamster cell line (HTG-2) was examined. In contrast to Moloney murine leukemia virus (M-MuLV) producing cell lines (MJD-54, clone 2) the amount of the Pr65gag remaining in the presence of cerulenin (20 micrograms/ml) was greatly reduced in both defective virus-infected cells. This effect appears specific for the Pr65gag polyprotein, since the env precursor polyprotein Pr80env was normally synthesized and remained undegraded in cerulenin-treated 3JE-infected cells. Thin-section electron micrographs showed an increased accumulation of virion particles in vesicles of treated HTG-2 cells.

Coordination of cleavage of gag and env gene products of murine leukemia virus: implications regarding the mechanism of processing

Mouse 3T6 cells infected with Murine Leukemia Virus (MuLV) were cloned to yield several sublines producing viruses distinct from one another with respect to the ratio of uncleaved to cleaved gag gene-coded polyprotein, Pr65gag. The virus produced by the cloned sublines also differed in the ratio of the env gene-coded protein, p15E, to its product, p12E. The two ratios, Pr65gag/p30 and p15E/p12E, were found to be highly correlated among the cloned cell lines. Velocity gradient separation of the virions produced by individual sublines, followed by polypeptide analysis, demonstrated that the particles were inhomogeneous with respect to extent of cleavage both of PR65gag and of p15E. The two cleavages were again highly correlated. These data indicate that the gag and env gene product cleavages are not independent events but are tightly coupled.

The cytoskeleton of murine leukemia virus (MuLV)-infected mouse fibroblasts as observed under varying conditions of formaldehyde fixation

Mouse fibroblasts chronically infected with Moloney murine leukemia virus (MuLV) were fixed using variable amounts of formaldehyde, then examined by indirect immunofluorescence light microscopy. Several antisera were employed to detect both external and internal antigens associated with the cells, eg, MuLV gp70, tubulin, vimentin, and actin. Our results indicate that the cell membranes could be partially permeabilized to IgG molecules directed against the three cytoskeletal antigens only after 3.7%, but not 1%, formaldehyde treatment. Complete permeabilization was achieved by subsequent acetone treatment of cells after 3.7% formaldehyde fixation. In such cells, normal-appearing cytoskeletal networks of microtubules and intermediate filaments were observed. Stress fibers were also seen; however, they appeared less numerous and thinner than those of uninfected mouse fibroblasts. Further, a significant amounts of F-actin fluorescence was localized in granules in the cytoplasm of infected cells. Similar observations were made using JLS-V9 mouse cells chronically infected with 334C virus, another MuLV. These results taken together suggest that subtle differences exist in the organization of actin within MuLV-infected and uninfected mouse fibroblasts.