SAK, A MURINE PROTEIN-SERINE THREONINE KINASE THAT IS RELATED TO THE DROSOPHILA-POLO KINASE AND INVOLVED IN CELL-PROLIFERATION/

We have isolated murine cDNAs encoding two isoforms of a putative prot ein-serine/threonine kinase, designated Sak-a and Sak-b, which differ in their noncatalytic C-terminal ends. The kinase domain of Sak is rel ated to the catalyic domains of the Drosophila polo, Saccharomyces cer evisiae CDC5, and murine Snk and Plk kinases, a family of proteins for which a role in controlling cell proliferation has been established ( polo, CDC5) or implicated (Snk, Plk). Northern and in situ RNA analyse s of Sak gene expression in mouse embryos and adult tissues revealed t hat expression was associated with mitotic and meiotic cell division. In addition, during embryogenesis, Sak expression was prominent in the respiratory and olfactory mucosa. The pattern of Sak expression and i ts sequence homology with the polo gene family suggest that the Sak ki nase may play a role in cell proliferation. In support of this, cell g rowth was suppressed by expression of a Sak-a antisense fragment in CH O cells.