Centromeres of the fission yeast Schizosaccharomyces pombe are highly variable genetic loci.

Abstract

Gross variations in the structure of the centromere of Schizosaccharomyces pombe chromosome II (cen3) were apparent following characterization of this centromeric DNA in strain Sp223 and comparison of the structure with that ofcen3 in three other commonly used laboratory strains. Further differences in centromere structure were revealed when the structure of the centromere ofS. pombe chromosome H (cen2) was compared among common laboratory strains and when the structures ofcen2 and cen3 from our laboratory strains were compared with those reported from other laboratories. Differences observed in cen3 structure include variations in the arrangement of the centromeric K repeats and an inverted orientation of the conserved centromeric central core. In addition, we have identified two laboratory strains that contain a minimal cen2 repeat structure that lacks the tandem copies of the cen2-specific block of K-L-B-J repeats characteristic of Sp223 cen2. We have also determined that certain centromeric DNA structural motifs are relatively conserved among the four laboratory strains and eight additional wild-type S. pombe strains isolated from various food and beverage sources. We conclude that in S. pombe, as in higher eukaryotes, the centromere of a particular chromosome is not a defined genetic locus but can contain significant variability. However, the basic DNA structural motif of a central core immediately flanked by inverted repeats is a common parameter of the S. pombe centromere.The centromere (cen) locus is a specialized region of eukaryotic chromosomal DNA that acts in conjunction with specific proteins to mediate chromosome segregation during mitotic and meiotic cell divisions. Centromere functions include maintenance of sister chromatid attachment during meiosis I and interaction, via the spindle attachment site or kinetochore, with mitotic and meiotic spindles, thereby ensuring proper segregation of chromosomes during cell divisions.Centromere DNAs of the budding yeast Saccharomyces cerevisiae have been extensively characterized, are only about 125 bp in length, and contain no repeated DNA sequences (5,8). Although analogous with respect to function, they appear structurally to be quite unlike the centromeres of higher eukaryotes, which in many cases contain extensive regions of heterochromatic repeated DNA, whose role is as yet unclear (2, 25). The genome of the fission yeast Schizosaccharomyces pombe is organized into only three chromosomes and provides an excellent alternate model system for studying the role of the centromere in cell division. The centromeres of S. pombe and those of higher eukaryotes have significant similarities that may be a reflection of their common mode of cell division. S. pombe centromeric regions are large, spanning approximately 40 to 100 kb of DNA, and consist in part of repetitive, nontranscribed DNA sequences that have been shown to play a role in centromere function (4,7,9,12,20). In addition, S. pombe centromeres are organized into a large inverted repeat (4, 7, 12) which...

Phylogenetic Analysis of Fungal Centromere H3 Proteins

“…Centromeres of the other Kluyveromyces/Saccharomyces yeasts are similar, differing only in the orientation of CDEI, the length of CDEII, and the specific sequence of CDEIII (Heus et al 1993;Iborra and Ball 1994;Kitada et al 1997). In contrast, S. pombe centromeres are 40-100 kbp in length and consist of 4-7 kbp AT-rich, nonhomologous central cores flanked by repetitive sequences (Steiner et al 1993). C. albicans centromeres resemble the S. pombe central cores, but lack the flanking repeats (Sanyal et al 2004), while Y. lipolytica centromeres are similar in size to those of S. cerevisiae but, aside from AT-richness, lack uniquely recognizable sequence motifs (Vernis et al 2001).…”

A novel cis-acting centromeric DNA element affects S. pombe centromeric chromatin structure at a distance.

“…The finding that the enhancer functions in either orientation is not surprising because K-type repeats are oriented differently with respect to the central core in the three S. pombe centromeres ( Fig. 1; Chikashige et al, 1989;Clarke and Baum, 1990;Hahnenberger et al, 1991;Steiner et al, 1993;Baum et al, 1994).…”

Centromeric DNA sequences in the pathogenic yeast Candida albicans are all different and unique

“…The fission yeast Schizosaccharomyces pombe centromere consists of a central core that is immediately flanked at both ends by a core-associated repeat (imr) organized in an inverted orientation (35,36). Repeats K͞dg and L͞dh extend the inverted repeat and, in addition, form direct-repeat arrays at cen2 and cen3.…”