MOLECULAR-CLONING AND EXPRESSION OF ALTERNATIVELY SPLICED PITSLRE PROTEIN-KINASE ISOFORMS

Minimal ectopic expression of the p58(GTA) protein kinase results in a provocative phenotype involving cell cycle delay, mitotic catastrophe , and decreased cell viability. In addition, this kinase is well conse rved evolutionarily, ubiquitously expressed, and its genes map to a po sition on human chromosome 1 frequently deleted in the late stages of tumorigenesis. Here we report that the p58(GTA) protein kinase is a me mber of a larger subfamily of proteins. The mRNAs encoding these prote ins are generated by alternative splicing from multiple duplicated gen es. These isoforms range in size from 50 to 110 kDa. Divergence betwee n the alternatively spliced isoforms is localized to the amino termina l region of the molecule. The entire p58(GTA) Open reading frame is co nserved in most of these p58(GTA) isoforms. The predicted sequences of the larger isoforms encode bipartite nuclear localization signal sequ ences and extensive polyglutamic acid domains. Antibodies to the p58(G TA) isoform were used to confirm the presence of the alternatively spl iced isoforms in different cell types as well as identify two addition al isoforms that appear to arise from a separate gene(s). Cellular fra ctionation studies indicate that one of the isoforms is found only in the nucleus, and the remainder are found in both the cytoplasm and the nucleus. Expression and localization of some p58(GTA) isoforms sugges t that they may have specialized cellular functions. Because of the la rge number of isoforms generated from multiple genes we propose naming these kinases PITSLRE alpha 1, alpha 2-1, alpha 2-2, alpha 2-3 alpha 2-4, beta 1, beta 2-1, and beta 2-2 based on the conserved sequence of the PSTAIRE box unique to p34(cdc2) kinases and the gene from which t hey are transcribed.