Diversity of tandemly repetitive sequences due to short periodic repetitions in the chromosomes of Candida albicans

Abstract

In a previous study, a repeated sequence, RPS1, was cloned from the genomic DNA of Candida albicans. It was 2.1 kb in length and was tandemly repeated in a limited region of almost all of the chromosomes. In this study, we examined and characterized the diversity of the repeating structure of the RPS units. RPS units were of 2.1, 2.3, 2.5, and 2.9 kbp in length after digestion of the genomic DNA with SmaI and 2.1 and 2.3 kbp after digestion with Pst1, with the differences being multiples of approximately 0.2 kbp. Moreover, one or two types of RPS unit were present specifically on each chromosome. We cloned 14 RPS units from the mixed DNA of chromosomes 1 and 2 and 59 RPS units from chromosome 6. These RPS units were classified into four types by their SfiI digestion profiles and chromosomal origins. Sequence comparisons revealed a tandem arrangement of internal, small repeating units of 172 bp. This unit of repetition was designated alt (C. albicans tandem repeating unit). The size of RPS units was variable, with sizes representing a series of increments of approximately 0.2 kbp that corresponded to the alt sequence. By contrast, the sequences other than the tandem repeats of alts were highly conserved, with homology of more than 98% among all cloned RPS units. These results suggested that RPS plays an important role in the organization and function of the chromosomes of C. albicans even though the actual function of RPS has not yet been clarified. Structural features of RPS that contains the repeated alt sequence are discussed in relation to human α-satellite DNA with its tandem repeats of about 170 bp that are similar in size to alt, the repetition of which is responsible for the variations in the size of the higher-order repeats.