The amino terminus of polyomavirus middle T antigen is required for transformation.
In polyomavirus-transformed cells, pp60c-src is activated by association with polyomavirus middle T antigen. These complexes have a higher tyrosine kinase activity compared with that of unassociated pp60c-src. Genetic analyses have revealed that the carboxy-terminal 15 amino acids of pp60c-src and the amino-terminal half of middle T antigen are required for this association and consequent activation of the tyrosine kinase. To define in greater detail the borders of the domain in middle T antigen required for activation of pp60c-src, we constructed a set of unidirectional amino-terminal deletion mutants of middle T antigen. Analysis of these mutants revealed that the first six amino acids of middle T antigen are required for it to activate the kinase activity of pp60c-src and to transform Rat-1 fibroblasts. Analysis of a series of insertion and substitution mutants confirmed these observations and further revealed that mutations affecting the first four amino acids of middle T antigen reduced or abolished its capacity to activate the kinase activity of pp60c-src and to transform Rat-1 cells in culture. Our results suggest that the first four amino acids of middle T antigen constitute part of a domain required for activation of the pp60c-src tyrosyl kinase activity and for consequent cellular transformation.
Cook
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DN
Department of Microbiology and Immunology, McGill University, Montreal, Quebec, Canada.
Hassell
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics*; D001483:Base Sequence; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002872:Chromosome Deletion; D008969:Molecular Sequence Data; D009154:Mutation; D015345:Oligonucleotide Probes; D010957:Plasmids; D011120:Polyomavirus / Q000235:genetics*; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D051381:Rats; D014162:Transfection
D000952:Antigens, Polyomavirus Transforming; D015345:Oligonucleotide Probes; D011505:Protein-Tyrosine Kinases