THE CENTROMERIC K-TYPE REPEAT AND THE CENTRAL CORE ARE TOGETHER SUFFICIENT TO ESTABLISH A FUNCTIONAL SCHIZOSACCHAROMYCES-POMBE CENTROMERE

The DNA requirements for centromere function in fission yeast have bee n investigated using a minichromosome assay system. Critical elements of Schizosaccharomyces pombe centromeric DNA are portions of the centr omeric central core and sequences within a 2.1-kilobase segment found on all three chromosomes as part of the K-type (K/K''/dg) centromeric repeat. The S. pombe centromeric central core contains DNA sequences t hat appear functionally redundant, and the inverted repeat motif that flanks the central core in all native fission yeast centromeres is not essential for centromere function in circular minichromosomes. Tandem copies of centromeric repeat K'', in conjunction with the central cor e, exert an additive effect on centromere function, increasing minichr omosome mitotic stability with each additional copy. Centromeric repea ts B and L, however, and parts of the central core and its core-associ ated repeat are dispensable and cannot substitute for K-type sequences . Several specific protein binding sites have been identified within t he centromeric K-type repeat, consistent with a recently proposed mode l for centromere/kinet-ochore function in S. pombe.