Cell cycle regulation of the human polo-like kinase (PLK) promoter

Plk (polo-like kinase) is a serine-threonine kinase that appears to function in mitotic control in mammalian cells. We demonstrated previously that PLK mRNA expression is low at the G₁-S transition, increases during S phase, and is maximally expressed during G₂-M. In the present study, we have cloned the human PLK gene and analyzed the structure and function of 2 kilobases of its 5'-flanking region. Using synchronized cultures of HeLa cells transfected with PLK promoter/luciferase constructs, we show that the promoter of PLK is activated at S phase and is maximal at G₂-M phase. Using various PLK promoter/luciferase constructs, we show that three activating regions are located between 35 and 93 base pairs upstream of the transcription initiation site. We identified a repressor element (CDE/CHR) in the region of the transcription start site, and mutations within this element diminished cell cycle regulation of transcription.