THE LYSINE-RICH C-TERMINAL REPEATS OF THE CENTROMERE-BINDING FACTOR-5(CBF5) OF KLUYVEROMYCES-LACTIS ARE NOT ESSENTIAL FOR FUNCTION

The gene coding for the centromere-binding factor 5 (CBF5) of Kluyvero myces lactis has been isolated by hybridization of a Saccharomyces cer evisiae CBF5 DNA probe to a K. lactis library. The amino acid sequence of KlCbf5 is highly homologous, 88% identity, to ScCbf5, but also to the rat protein Nap57 (64% identity). The main difference between both yeast proteins and the rat protein is the presence of a lysine-rich d omain with KKE/D repeats in the C-terminal part of the protein. These repeats are thought to be involved in binding of the protein to microt ubules. Deletion of the KKE/D domain in KlCbf5 however, has no discern ible effect on growth on rich medium, sensitivity to the microtubule-d estabilizing drug benomyl or segregation of a reporter plasmid. On the other hand, insertion of two leucine residues adjacent to the KKE dom ain increases the loss rate of a reporter plasmid. In both yeasts comp lementation of a lethal CBF5 disruption with the heterologous gene res ults in a slight increase in benomyl sensitivity. A possible role of C BF5 in chromosome segregation will be discussed. (C) 1998 John Wiley & Sons, Ltd.