Site-directed deletions of Abelson murine leukemia virus define 3' sequences essential for transformation and lethality

Abstract

Abelson murine leukemia virus (A-MuLV) encodes a single protein with tyrosine kinase activity that can transform fibroblast cell lines in vitro and lymphoid target cells in vitro and in vivo. Expression of kinase-active A-MuLV protein can result in a deleterious effect on transformed fibroblast populations, leading to cell death or selection for nonlethal mutants of the virus. These mutants retain expression of the kinase activity but have lost large portions of the carboxy terminus of the Abelson protein. To more precisely map the sequences involved in this lethal effect, we have isolated a series of site-directed deletions from a DNA clone of the P160 wild-type strain of A-MuLV. In addition, a number of unexpected, spontaneous deletions occurring during transfection of NIH 3T3 cells were isolated. These deletions result in expression of carboxy-terminal truncated forms of the A-MuLV protein ranging from 130,000 to 84,000 in molecular weight. Analysis of the transforming and lethal activities of each mutant recovered in its RNA viral form shows that the transformation-essential and lethal-essential sequences do not overlap. These data and our previous work suggest that a function carried by the carboxy-terminal region of the A-MuLV protein acts in cis with the kinase-essential region to mediate the lethal effect.