Cohesion between sister chromatids mediated by a multisubunit complex called 
cohesin is established during DNA replication and is essential for the orderly 
segregation of chromatids during anaphase. In budding yeast, a specialized 
replication factor C called RF-C(Ctf18/Dcc1/Ctf8) and the 
DNA-polymerase-alpha-associated protein Ctf4 are required to maintain 
sister-chromatid cohesion in cells arrested for long periods in mitosis. We show 
here that CTF8, CTF4 and a helicase encoded by CHL1 are required for efficient 
sister chromatid cohesion in unperturbed mitotic cells, and provide evidence 
that Chl1 functions during S-phase. We also show that, in contrast to mitosis, 
RF-C(Ctf18/Dcc1/Cft8), Ctf4 and Chl1 are essential for chromosome segregation 
during meiosis and for the viability of meiotic products. Our finding that cells 
deleted for CTF8, CTF4 or CHL1 undergo massive meiosis II non-disjunction 
suggests that the second meiotic division is particularly sensitive to cohesion 
defects. Using a functional as well as a cytological assay, we demonstrate that 
CTF8, CHL1 and CTF4 are essential for cohesion between sister centromeres during 
meiosis but dispensable for cohesin's association with centromeric DNA. Our 
finding that mutants in fission yeast ctf18 and dcc1 have similar defects 
suggests that the involvement of the alternative RF-C(Ctf18/Dcc1/Ctf8) complex 
in sister chromatid cohesion might be highly conserved.