A DIRECT LINK BETWEEN SISTER-CHROMATID COHESION AND CHROMOSOME CONDENSATION REVEALED THROUGH THE ANALYSIS OF MCD1 IN SACCHAROMYCES-CEREVISIAE

The S. cerevisiae MCD1 (mitotic chromosome determinant) gene was ident ified in genetic screens for genes important for chromosome structure. MCD1 is essential for viability and homologs are found from yeast to humans. Analysis of the mcd1 mutant and cell cycle-dependent expressio n pattern of Mcd1p suggest that this protein functions in chromosome m orphogenesis from S phase through mitosis. The mcd1 mutant is defectiv e in sister chromatid cohesion and chromosome condensation. The physic al association between Mcd1p and Smc1p, one of the SMC family of chrom osomal proteins, further suggests that Mcd1p functions directly on chr omosomes. These data implicate Mcd1p as a nexus between cohesion and c ondensation. We present a model for mitotic chromosome structure that incorporates this previously unsuspected link.