CELL-CYCLE REGULATION OF THE HUMAN POLO-LIKE KINASE (PLK) PROMOTER

Plk (polo-like kinase) is a serine-threonine kinase that appears to fu nction in mitotic control in mammalian cells. We demonstrated previous ly that PLK mRNA expression is low at the G(1)-S transition, increases during S phase, and is maximally expressed during G(2)-M. In the pres ent study, we have cloned the human PLK gene and analyzed the structur e and function of 2 kilobases of its 5'-flanking region. Using synchro nized cultures of HeLa cells transfected with PLK promoter/luciferase constructs, we show that the promoter of PLK is activated at S phase a nd is maximal at G(2)-M phase. Using various PLK promoter/luciferase c onstructs, we show that three activating regions are located between 3 5 and 93 base pairs upstream of the transcription initiation site. We identified a repressor element (CDE/CHR) in the region of the transcri ption start site, and mutations within this element diminished cell cy cle regulation of transcription.