Journal of General Microbiology zyxwvutsrqpo (1992), zyxwvutsrq 138, 1893-1900. Printed in Great Britain 1893 z Isolation and characterization of a repeated sequence (RPS1) of zy Candida albicans SHIN-ICHI IWAGUCHI, MICHIO HOMMA,* HIROJI CHIBANA and KENJI TANAKA Laboratory of Medical Mycology, Research Inslitute zyxwvu for Disease Mechanism and Control, Nagoya University School of Medicine, Showa-ku, Nagoya 466, Japan (Received zyxwvutsrqpo 22 January 1992; revised 1 May 1992; accepted 10 June 1992) A repeated sequence, named RPSl, approximately 2 kb in size, is found mainly in chromosome 6, the second most variable chromosome among the eight chromosomes of Candida albicans. Most of the RPSl units of chromosome 6 seem to be located within a single region of about 100 kb in strain FC18. In both strains FC18 and NUM812, a part of RPSl is apparently tandemly repeated. A unit of RPSl has been cloned and sequenced. It consists of 2114 bp and has a GC content of zyxwvuts 40 mol%. The repeat unit contains smaller repeats of about 80-170 bp which are called REP1, REP2, REP3, REP4 and REPS; REP2 is duplicated. The small repeats are classified into two groups by their homology. One comprises REP1, REP2 and REPS, and the other REP3 and REP4. They are termed the REP1 and REP3 families, respectively. The two families both contain a common 29 bp sequence, called COM29. The dispersed repetitive sequence RE1 may be involved in chromosomal rearrangements and may in part explain chromosome polymorphism in C. albicans. The origin of RPSl was not determined. Introduction The imperfect yeast Candida albicans, which is an opportunistic pathogen, exists as a diploid in all known strains; the haploid state has not yet been found (Scherer zyxwvu & Magee, 1990). C. albicans contains eight pairs of homologous chromosomes (Iwaguchi et al., 1990;Lasker et al., 1989; Wickes et al., 1991). Chromosome size- variation has been detected in this species (Lott et al., 1987; Magee & Magee, 1987; Merz et al., 1988; Snell et al., 1987; Iwaguchi et al., 1990). In our previous study (Iwaguchi et al., 1990), the chromosomal DNAs of C. albicans were resolved into 7-12 bands ranging in size from about 0-4 Mb to about 3-0 Mb by pulsed-field gel electrophoresis (PFGE) and no two strains showed an identical electrophoretic karyotype. Of the eight C. albicans chromosomes, chromosome 2, assigned by a MGLl probe, was more variable in size than the other * Author for correspondence.Tel. 052-741-21 11 (ext. 21 16); fax 052- 731-9479. Abbreviation : PFGE, pulsed-field gel electrophoresis. The nucleotide sequence data reported in this paper have been submitted to GenBank and have been assigned the accession number M87288. chromosomes. The karyotypes of the isolates recovered from individual patients after intervals of 1-6 months were virtually identical; however, one or two chromo- somes were variable in size (Asakura et al., 1991). In virtually all cases, the chromosome that varied in size was chromosome 2. This suggested that chromosome 2 is too variable to be useful for distinguishing between strains. A similar variable chromosome was also ob- served by Rustchenko-Bulgac (1991) and Wickes et al. (1991) in different strains. More than 10% of clones of our strains exhibit a change in the size of chromosome 2 (Iwaguchi et al., 1992). Chromosome 2 carries an rDNA gene. The rDNA gene sequence is usually highly repeated within a single chromosomal region, in which DNA rearrangement occurs at a high frequency (Szostak & Wu, 1980). We have confirmed the assumption that the clonal size-variation of chromosome 2 is derived from the rDNA cluster size-change by this type of rearrange- ment (Iwaguchi et al., 1992). We found that chromosome 6, assigned by a pTK2-9-1 probe which was prepared from a cloned DNA fragment, was the second most variable in size (Iwaguchi et al., 1990). Chromosome 6 did not always strongly hybridize to a probe which was prepared from whole chromosome 6 DNA. This difference between the fragment probe and the whole chromosome was thought to be due to the presence of a repeated sequence in 0001-7357 O 1992 SGM