CENTROMERE PROMOTER FACTORS (CPF1) OF THE YEASTS SACCHAROMYCES-CEREVISIAE AND KLUYVEROMYCES-LACTIS ARE FUNCTIONALLY EXCHANGEABLE, DESPITE LOW OVERALL HOMOLOGY

The KlCPF1 gene, coding for the centromere and promoter factor CPF1 fr om Kluyveromyces lactis, has been cloned by functional complementation of the methionine auxotrophic phenotype of a Saccharomyces cerevisiae mutant lacking ScCPF1. The amino-acid sequences of both CPF1 proteins show a relatively-low overall identity (31%), but a highly-homologous C-terminal domain (86%). This region constitutes the DNA-binding doma in with basic-helix-loop-helix acid leucine-zipper motifs, features co mmon to the myc-related transcription factor family. The N-terminal tw o-thirds of the CPF1 proteins show no significant similarity, although the presence of acidic regions is a shared feature. In KlCPF1, the ac idic region is a prominent stretch of approximately 40 consecutive asp artate and glutamate residues, suggesting that this part might be invo lved in transcriptional activation. In-vitro mobility-shift experiment s were used to establish that both CPF1 proteins bind to the consensus binding site RTCACRTG (CDEI element). In contrast to S. cerevisiae, C PF1 gene-disruption is lethal in K. lactis. The homologous CPF1 genes were transformed to both S. cerevisiae and K. lactis cpf1-null strains . Indistinguishable phenotypes were observed, indicating that, not wit hstanding the long nonconserved N-terminal region, the proteins are su fficiently homologous to overcome the phenotypes associated with cpf1 gene-disruption.