Separation of host range from transformation functions of the hr-t gene of polyomavirus.
hr-t mutants of polyomavirus are defective in virus growth as well as in cell transformation, and have genetic alterations that invariably affect both the middle and small T proteins. We have examined the growth properties of three site-directed mutants that either eliminate or alter the middle T without affecting the small T protein. Mutant 808A encodes large and small T proteins but no middle T; it grew poorly in NIH 3T3 cells. In contrast, mutants 1387T and 1178T which express altered middle T along with normal large and small T proteins grew nearly as well as wild-type virus. Thus, although the altered middle T proteins encoded by 1387T and 1178T are defective for cell transformation, they retained the ability to induce expression of a cellular permissivity factor(s) required for virus production. At the biochemical level, the induction of permissivity by middle T was manifested primarily in terms of phosphorylation of VP1 on threonine and in efficient encapsidation of viral DNA to form infectious virus. The natural role of middle T involves regulation of phosphorylation events, and can be enacted, at least in part, independently of interactions with pp60c-src.
Garcea
R L
RL
Division of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
Talmage
D A
DA
Harmatz
A
A
Freund
R
R
Benjamin
T L
TL
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002472:Cell Transformation, Viral; D004279:DNA, Viral / Q000096:biosynthesis; D005814:Genes, Viral; D009154:Mutation; D010766:Phosphorylation; D011120:Polyomavirus / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D014764:Viral Proteins / Q000378:metabolism; D015678:Viral Structural Proteins
D000952:Antigens, Polyomavirus Transforming; D004279:DNA, Viral; D014764:Viral Proteins; D015678:Viral Structural Proteins