A novel sequence common to the centromere regions ofSchizosaccharomyces pombechromosomes

An approximately 4 kb long sequence (designated dh) is located in the centromere regions of all three chromosomes of S. pombe. There is one copy each of dh per centromere in chromosomes I and II and multiples in the centromere of chromosome III. Nucleotide sequence determination shows that dhI and dhII are highly homologous. A part of the sequence (ca. 300-400 bp) contains short direct repeats, otherwise dh is in general internally non-repetitious. Although there are three segmental deletions (total 821 bp) and two insertions (27 bp) in dhII (an 80% overall homology to dhI), there are only nine substitutions between dhI and dhII in the remaining 3980 bp, giving a 99.77% homology. The substitutions are restricted to the non-repetitious domains and are only of the pyrimidine-pyrimidine or purine-purine types. A possible conformational role of dh is discussed.