The mouse Plk gene: structural characterization, chromosomal localization and identification of a processed Plk pseudogene

Abstract

The Plk gene encodes a serine/threonine protein kinase believed to be important for the normal progression of mammalian cells through the cell cycle. In this paper, we report the genomic organization of the mouse Plk gene. The mouse Plk gene encompasses 16 kb of the mouse genome and is organised into 10 exons. Based on homology with the human PLK1 promoter region, the putative mouse promoter region includes a CCAAT motif but lacks the conventional TATA motif. The proposed promoter region contains consensus binding sites for several transcriptional regulators, including Sp1 and AP2. In addition to the active copy of Plk, Plk exists as a processed pseudogene. Using RFLP analysis, we have localized the active Plk gene to mouse Chromosome 7 and the processed pseudogene to mouse Chromosome 5. Southern blot analysis of DNA from a limited number of other mammalian species suggests that the duplication is confined to the mouse. Parsimony analysis suggests that the gene duplication leading to the mouse Plk pseudogene occurred after the rat–mouse split.

Introduction

The Plk gene encodes a member of the polo subfamily of protein serine/threonine kinases (Clay et al., 1993; Hamanaka et al., 1994; Lake and Jelinek, 1993). Plk is expressed in the foetal and adult mouse in cells or tissues undergoing cell proliferation (Clay et al., 1993). The Plk gene product has been implicated in the regulation of mitotic spindle function; it appears to function as an M-phase specific protein kinase required for passage through the cell cycle (Golsteyn et al., 1995; Lee et al., 1995). To date, four murine members of the polo subfamily have been identified. The Plk, Fnk, Snk and Sak proteins are all expressed in a variety of cell types undergoing active cell proliferation (Clay et al., 1993; Simmons et al., 1993; Fode et al., 1994; Hamanaka et al., 1994; Donohue et al., 1995). Protein kinases of the polo subfamily have been identified from a number of different species, including human, rat, Drosophila, Xenopus and yeast (Llamazares et al., 1991; Hamanaka et al., 1994; Holtrich et al., 1994; Okhura et al., 1995; Li et al., 1996; Kumagai and Dunphy, 1996). Members of the polo subfamily share a similar overall structure and exhibit a high degree of sequence conservation both in the kinase domain and in the 3′ extracatalytic region, suggesting that these molecules share a close functional and evolutionary relationship.

The aim of the current study was to determine the genomic structure of the mouse Plk gene as a prelude to undertaking a targeted disruption of the Plk gene. In the course of this work, we discovered that in addition to the active copy of Plk, Plk also exists as a processed pseudogene. This paper examines the structure and chromosomal localization of both the active mouse Plk gene and the processed pseudogene.