title: N-terminal amino acid sequences of the polyoma middle-size T antigen are important for protein kinase activity and cell transformation.
abstract: We constructed deletion mutations which removed N-terminal coding sequences of various lengths from a cloned polyoma middle-size T antigen (MT antigen) gene. We introduced the MT antigen genes into a simian virus 40 expression vector so that they were expressed at high levels under the control of the simian virus 40 late promoter in COS-1 cells. The deletion mutant genes synthesized truncated MT antigens whose size was consistent with the deletion of either 70 or 106 amino acids from N termini, owing to initiation of translation at internal methionine codons in the MT antigen-coding region. The truncated MT antigens were found in cell membrane fractions but failed to show MT antigen-associated protein kinase activity. The cloned deletion mutant DNAs failed to transform rat F2408 or mouse NIH 3T3 cells. Therefore, N-terminal amino acid sequences of the polyoma MT antigen, as well as C-terminal sequences, are important for protein kinase activity and cell transformation.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D001483:Base Sequence; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D002872:Chromosome Deletion; D003001:Cloning, Molecular; D005796:Genes; D005814:Genes, Viral; D005822:Genetic Vectors; D007668:Kidney; D051379:Mice; D009154:Mutation; D010957:Plasmids; D011120:Polyomavirus / Q000235:genetics*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D014764:Viral Proteins; D011494:Protein Kinases