CLONING AND CHARACTERIZATION OF HUMAN AND MURINE HOMOLOGS OF THE DROSOPHILA POLO SERINE-THREONINE KINASE

We have cloned both human and murine complementary DNAs that are homol ogous to the Drosophila serine/threonine polo kinase and the recently cloned murine polo related kinase (PLK). Both the human and murine clo nes are about 2.1 kilobases with open reading frames of 1.8 kilobases, encoding proteins of 603 amino acids with a predicted size of 66 kilo daltons and an apparent size of 67 kilodaltons by sodium dodecyl sulfa te-polyacrylamide gel electrophoresis analysis. During embryonic devel opment of the mouse, the mRNA was expressed in all tissues examined, w hereas in adult tissues, expression was limited to thymus and ovaries. All cell lines examined also expressed mRNAs of similar size. Microin jection of in vitro transcribed sense mRNA into serum-starved murine N IH3T3 cells induced tritiated thymidine incorporation, whereas microin jection of antisense RNA into growing NIH3T3 cells blocked tritiated t hymidine incorporation. When PC12 rat cells were induced to differenti ate with nerve growth factor, gene expression of PLK was greatly reduc ed. Together, these results suggest that PLK expression is restricted to, and is perhaps required by, proliferating cells.