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.