A murine leukemia virus mutant with a temperature-sensitive defect in membrane glycoprotein synthesis

Cells infected with a temperature-sensitive mutant (ts-26) of Rauscher murine leukemia virus (R-MuLV) or with wild-type virus were labeled with ³⁵S-methionine, and cell extracts were examined for radioactive polypeptides which could be precipitated by monospecific antisera to viral proteins. When shifted from permissive (31°C) to nonpermissive (39°C) temperature, cells infected with ts-26 rapidly begin to accumulate gPr90^enr, the glycoprotein precursor to the membrane envelope glycoprotein gp70 and to the membrane-associated protein p15E. Simultaneously, formation of these mature virion proteins ceases. In addition, lactoperoxidase-catalyzed surface labeling with ¹²⁵I-iodine indicates that the plasma membrane of cells infected with ts-26 becomes depleted of gp70 antigens at 39°C. Nevertheless, at 39°C these cells release defective MuLVs which lack gp70 and p15E but contain an outer membrane. The release particles also contain an aberrantly processed form of the major virion core protein p30, and many of these virion cores have an unusual immature crescent shape. It has previously been reported that cells infected with the ts-26 mutant of R-MuLV process a 65,000 dalton precursor (Pr65^gag) of the virion core proteins more slowly at 39°C than do cells infected with wild-type virus (Stephenson, Tronick and Aaronson, 1975). Although we have confirmed these results, this effect is relatively small and it is known that various alterations of MuLV assembly can lead secondarily to inhibited processing of Pr65^gag. We propose that the ts-26 mutant has a primary temperature-sensitive defect in membrane glycoprotein synthesis and that this change causes pleiotropic effects on core morphogenesis.