A low copy number central sequence with strict symmetry and unusual chromatin structure in fission yeast centromere.

Abstract

Fission yeast centromeres vary in size but are organized in a similar fashion. Each consists of two distinct domains, namely, the -15-kilobase (kb) central region (cnt + imr), containing chromosome-specific low copy number sequences, and 20-to 100-kb outer surrounding sequences (otr) with highly repetitive motifs common to all centromeres. The central region consists of an inner asymmetric sequence flanked by inverted repeats that exhibit strict identity with each other. Nucleotide changes in the left repeat are always accompanied with the same changes in the right. The chromatin structure of the central region is unusual. A nucleosomal nuclease digestion pattern formed on unstable plasmids but not on stable chromosome. DNase I hypersensitive sites correlate with the location of tRNA genes in the central region. Autonomously replicating sequences are also present in the central region. The behavior of truncated minichromosomes suggested that the central region is essential, but not sufficient, to confer transmission stability. A portion of the outer repetitive region is also required. A larger outer region is necessary to ensure correct meiotic behavior. Fluorescence in situ hybridization identified individual cens. In the interphase, they cluster near the nuclear periphery. The central sequence (cnt + imr) may play a role in positioning individual chromosomes within the nucleus, whereas the outer regions (otr) may interact with each other to form the higher-order complex structure.

Tripartite organization of centromeric chromatin in budding yeast

“…S9) confirms previous findings of centromere hypersensitivity to MNase digestion in Schizosaccharomyces pombe (37) and Drosophila (8). This low recovery also raises questions about reports of what appear to be conventional CenH3 octameric nucleosomes isolated from diverse eukaryotes (38,39), because these particles were extracted under conditions that led to depletion of yeast centromeric chromatin, which we might attribute to catastrophic loss by cleavage within the singly wrapped CenH3 particle.…”

NDC10: a gene involved in chromosome segregation in Saccharomyces cerevisiae

“…In S. cerevisiae Peterson and Ris (1976) mapped the position of discontinuous, probably chromosomal, microtubules. In Saprolegnia kinetochore position was mapped by EM throughout the cell cycle (Heath, 1980a;Heath and Rethoret, 1981), and in S. pombe preliminary experiments have mapped centromere position using DNA probes (Uzawa and Yanagida, 1992;Takahashi et al, 1992). If these three sets of results are combined, then some tentative conclusions can be drawn about kinetochore position during the cell cycle in S. cerevisiae.…”

The Role of Model Organisms in the History of Mitosis Research

“…Analyses of artificially constructed minichromosomes by pulsed-field gel electrophoresis showed that the size of the S. pombe centromere is 30-to 130-kb long, much larger than that of S. cerevisiae, which is on the order of 0.1 kb Hahnenberger et al 1991;Takahashi et al 1992). Linear minichromosomes were obtained by double truncation followed by the addition of telomeric sequences.…”

“…The circular minichromosomes were isolated by the gap-repair method (Hahnenberger et al 1989;Niwa et al 1989). These 30-to 160-kb minichromosomes were useful to define the S. pombe functional centromere re-gions and also to determine the entire repetitious centromere sequence Takahashi et al 1992). The pericentromeric repeats are heterochromatic because histone H3 is methylated and heterochromatin protein 1 (HP-1), which affects accurate chromosome segregation like Swi6, is abundant.…”