THE EXPRESSION OF THE ESSENTIAL GENE KRR1 (YCL059c) IS DEPENDENT ON GENE DOSAGE AND GROWTH CONDITIONS

R. Gromadka¹, A. Kaniak², P.P. Slonimski², J. Rytka¹

¹Institute of Biochemistry and Biophysics, Polish Academy of Science, Pawiñskiego 5a, 02-106, Warsaw, Poland

² Centre de Genetique Moleculaire, CNRS, F-91198 Gif-sur-Yvette, France

The newly discovered Saccharomyces cerevisiae gene KRR1 (YCL059c) of unknown function, is essential for cell growth. The sequence predicts a protein of 317 amino acids, including a region of 131 amino acids which is highly conserved between evolutionary distant species: yeast, nematode, plants and human. The conserved region contains a cluster of basic amino acids (KRR), which may act as a nuclear targeting sequence.

The codon bias of the gene (0.25), suggested that it should be relatively well expressed. This has been confirmed by a Northern blot analysis which showed that KRR1 was expressed at about 10% of the level of actin (ACT1) in cells growing on rich glucose medium. When cloned on a multicopy plasmid the transcript level increases dramatically, but this has no effect on cell growth. To further understand the regulation of the gene, we have constructed an in phase fusion between the promotor region and the first 121 codons of the KRR1 gene and the LacZ gene in the vector YIp367. This construction has been integrated at the LEU2 locus of both haploid and diploid strains, data concerning the expression of -galactosidase in these strains under different growth conditions will be presented.