The Condensin Complex Governs Chromosome Condensation and Mitotic Transmission of Rdna

Abstract

We have characterized five genes encoding condensin components in Saccharomyces cerevisiae. All genes are essential for cell viability and encode proteins that form a complex in vivo. We characterized new mutant alleles of the genes encoding the core subunits of this complex, smc2-8 and smc4-1. Both SMC2 and SMC4 are essential for chromosome transmission in anaphase. Mutations in these genes cause defects in establishing condensation of unique (chromosome VIII arm) and repetitive (rDNA) regions of the genome but do not impair sister chromatid cohesion. In vivo localization of Smc4p fused to green fluorescent protein showed that, unexpectedly, in S. cerevisiae the condensin complex concentrates in the rDNA region at the G2/M phase of the cell cycle. rDNA segregation in mitosis is delayed and/or stalled in smc2 and smc4 mutants, compared with separation of pericentromeric and distal arm regions. Mitotic transmission of chromosome III carrying the rDNA translocation is impaired in smc2 and smc4 mutants. Thus, the condensin complex in S. cerevisiae has a specialized function in mitotic segregation of the rDNA locus. Chromatin immunoprecipitation (ChIP) analysis revealed that condensin is physically associated with rDNA in vivo. Thus, the rDNA array is the first identified set of DNA sequences specifically bound by condensin in vivo. The biological role of higher-order chromosome structure in S. cerevisiae is discussed.

Transcriptional homogenization of rDNA repeats in the episome-based nucleolus induces genome-wide changes in the chromosomal distribution of condensin

“…Chromatin-binding assays were as described (Liang and Stillman, 1997). Anti-condensin antibodies have been described (Freeman et al, 2000).…”

“…Eukaryotic condensin complex subunits are conserved from yeast to human (Fujimoto et al, 2005;Hirano, 2005). In budding yeast Saccharomyces cerevisiae, the condensin complex is composed of five polypeptides, including the SMC heterodimer (Smc2p and Smc4p) and three non-SMC subunits (Brn1p, Ycs4p and Ycs5p/Ycg1p) (Freeman et al, 2000). Similar complexes exist in higher eukaryotes (Hirano et al, 1997;Schmiesing et al, 1998;Sutani et al, 1999;Freeman et al, 2000;Kimura et al, 2001).…”

“…In budding yeast Saccharomyces cerevisiae, the condensin complex is composed of five polypeptides, including the SMC heterodimer (Smc2p and Smc4p) and three non-SMC subunits (Brn1p, Ycs4p and Ycs5p/Ycg1p) (Freeman et al, 2000). Similar complexes exist in higher eukaryotes (Hirano et al, 1997;Schmiesing et al, 1998;Sutani et al, 1999;Freeman et al, 2000;Kimura et al, 2001). Dysfunction of any condensin subunit results in impaired mitotic and meiotic chromosome segregation (Strunnikov et al, 1995;Bhat et al, 1996;Freeman et al, 2000;Ouspenski et al, 2000;Hagstrom et al, 2002;Hudson et al, 2003;Ono et al, 2003;Cobbe et al, 2006).…”

“…The ribosomal RNA gene cluster (rDNA) in S. cerevisiae is the major identified target of condensin binding, and it is particularly enriched in condensin during mitosis (Freeman et al, 2000;Wang et al, 2005). Incidentally, condensin's activity was shown to be especially important for segregation of the rDNA-containing chromosome XII (Freeman et al, 2000;D'Amours et al, 2004;Sullivan et al, 2004;Wang et al, 2004;Machin et al, 2005) as well as other chromosomes, if they contain rDNA inserts (Freeman et al, 2000).…”

“…Incidentally, condensin's activity was shown to be especially important for segregation of the rDNA-containing chromosome XII (Freeman et al, 2000;D'Amours et al, 2004;Sullivan et al, 2004;Wang et al, 2004;Machin et al, 2005) as well as other chromosomes, if they contain rDNA inserts (Freeman et al, 2000). Mitotic condensin enrichment in nucleolar chromatin apparently occurs without additional condensin synthesis, by its relocalization from non-rDNA sites .…”