Mutant of B-tropic murine leukemia virus synthesizing an altered polymerase molecule

Abstract

A nonconditional mutant of B-tropic murine leukemia virus (MuLV), defective in polymerase, has been isolated by cloning chronically infected cells. The cell clone containing the mutant produced virus particles which were noninfectious. However, superinfection of the cells by replication-competent XC-negative viruses resulted in the rescue of virus capable of forming plaques in a modified XC test, termed the "complementation plaque assay" (A. Rein and R. H. Bassin, J. Virol. 28:656-660, 1978). Analysis of the noninfectious virions produced without superinfection demonstrated that they contained only 2 to 5% of the wild-type level of reverse transcriptase activity. Purification of this activity indicated that it was associated with a smaller molecule than that produced by wild-type virus. Cells producing the mutant virions did not contain the gag-pol precursor, Pr1809"'-1°'; however the cells contained proteins of 147K and 114K daltons precipitable with anti-pol serum. All of the normal structural proteins as well as 70S genomic RNA could be detected in the mutant particles. An interference test indicated that a functional ecotropic glycoprotein was synthesized by the mutant. These results indicate that the mutant has a unique defect in the pol gene.

Replication-defective Friend murine leukemia virus particles containing uncleaved gag polyproteins and decreased levels of envelope glycoprotein

“…The lack of this precursor protein and the presence of antigenically related proteins with unusual molecular weights were found in another defective MuLV which made no active reverse transcriptase (17). From the present data, it is difficult to tell whether the 70,000-dalton protein in 7C virus is gag or pol or related to both gene products.…”

Mechanism of restriction of murine leukemia viruses varies between different strains of Fv‐1n mice

“…In particular, a BALB/3T3 cell is able to restrict the replication of a single Ntropic MuLV particle with high efficiency, but the mechanism of inactivation is such that the cellular Fv-1 restriction system itself is abrogated, and the cell is rendered permissive to infection with a second N-tropic MuLV particle. Abrogation of Fv-lb restriction depends on the functioning of part, but not all, of the viral genome, but does not require reverse transcriptase activity or DNA synthesis (Gerwin et al, 1979;Bassin et al, 1978, and manuscript in preparation). Abrogation is transient and can be demonstrated between 3 and 18 h after the infection of BALB/3T3 cells with restricted MuLV (Duran-Troise et Bassin et al, 1978).…”

“…Anothcr characteristic of abrogation in BALB/3T3 cells is its time-dependence (Niwa et al, 1976;Duran-Troise et al. 1977;Bassin et a/., 1978Bassin et a/., , 1979. It takes about 6 h for MuLV to abrogate Fv-lb restriction after infection of BALB/3T3 cells, and the effect lasts for about 18 h after which the cells again exhibit Fv-1 restriction.…”

Four Moloney murine leukemia virus-infected rat cell clones producing replication-defective particles: protein and nucleic acid analyses

“…Other murine replication mutants include those which are defective in reverse transcriptase. An M-MuLV variant that packages a smaller polymerase in its virions has been reported by Gerwin et al (10). Still other murine mutants in reverse transcriptase include those which produce no Pr1809'9"P" precursor and hence no reverse transcriptase in viral particles (24).…”