Human SAK related to the PLK/polo family of cell cycle kinases shows high mRNA expression in testis.

We identified the nucleotide sequence of a cDNA encoding a polypeptide with a kinase domain that is related to the catalytic region of Drosophila melanogaster polo, Saccharomyces cerevisiae CDC5 as well as human FNK and PLK. The novel gene seems to represent the human counterpart of the mouse gene sak. The sequence of SAK predicts a serine/threonine kinase of 970 aa. The distribution of SAK mRNA in adult organs is restricted to certain tissues such as testis and thymus. Northern analyses of tumor tissues (lung, breast, brain) and corresponding normal tissues from the same patient did not reveal SAK expression. Comparing the mRNA distribution of the proliferation-associated polo-like kinase (PLK) with the expression of SAK we observed distinct differences. Thus, we suggest that these kinases have unique physiological roles in different cells or in response to different signals.