In eukaryotic cells, faithful chromosome segregation depends upon the physical pairing, or cohesion, between sister chromatids. Budding yeast CTF7/ECO1 (herein termed CTF7) encodes an essential protein required to establish cohesion during S-phase and associates with DNA replication factors [1.Skibbens R.V. Corson L.B. Koshland D. Hieter P. Ctf7p is essential for sister chromatid cohesion and links mitotic chromosome structure to the DNA replication machinery.Genes Dev. 1999; 13: 307-319Crossref PubMed Scopus (372) Google Scholar, 2.Toth A. Ciosk R. Uhlmann F. Galova M. Schleiffer A. Nasmyth K. Yeast cohesin complex requires a conserved protein, Eco1p(Ctf7), to establish cohesion between sister chromatids during DNA replication.Genes Dev. 1999; 13: 320-333Crossref PubMed Scopus (486) Google Scholar, 3.Mayer M.L. Gygi S.P. Aebersold R. Hieter P. Identification of RFC (Ctf18p, Ctf8p, Dcc1p): An alternate RFC complex required for sister chromatid cohesion in S. cerevisiae.Mol. Cell. 2001; 7: 959-970Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar, 4.Hanna J.S. Kroll E.S. Lundblad V. Spencer F.A. Saccharomyces cerevisiae CTF18 and CTF4 are required for sister chromatid cohesion.Mol. Cell. Biol. 2001; 21: 3144-3158Crossref PubMed Scopus (251) Google Scholar, 5.Wang Z. Castano I.B. De Las Penas A. Adams C. Christman M.F. Pol kappa: A DNA polymerase required for sister chromatid cohesion.Science. 2000; 289: 774-779Crossref PubMed Scopus (160) Google Scholar, 6.Krause S.A. Loupart M.L. Vass S. Schoenfelder S. Harrison S. Heck M.M. Loss of cell cycle checkpoint control in Drosophila Rfc4 mutants.Mol. Cell. Biol. 2001; 21: 5156-5168Crossref PubMed Scopus (40) Google Scholar, 7.Kenna M.A. Skibbens R.V. Mechanical link between cohesion establishment and DNA replication: Ctf7p/Eco1p, a cohesion establishment factor, associates with three different Replication Factor C Complexes.Mol. Cell. Biol. 2003; 23: 2999-3007Crossref PubMed Scopus (90) Google Scholar, 8.Edwards S. Li C.M. Levy D.L. Brown J. Snow P.M. Campbell J. Saccharomyces cerevisiae DNA polymerase varepsilon and polymerase sigma interact physically and functionally, suggesting a role for polymerase varepsilon in sister chromatid cohesion.Mol. Cell. Biol. 2003; 23: 2733-2748Crossref PubMed Scopus (75) Google Scholar, 9.Skibbens R.V. Chl1p, a DNA helicase-like protein in budding yeast, functions in sister chromatid cohesion.Genetics. 2004; 166: 32-42Crossref Scopus (123) Google Scholar, 10.Petronczki M. Chwalla B. Siomos M. Yokobayashi S. Helmhart W. Deutschbauer A. et al.Sister-chromatid cohesion mediated by the alternative RF-CCtf18/Dcc1/Ctf8, the helicase Chl1 and the polymerase-alpha-associated protein Ctf4 is essential for chromatid disjunction during meiosis II.J. Cell Sci. 2004; 117: 3547-3559Crossref PubMed Scopus (115) Google Scholar]. However, the molecular mechanism by which Ctf7p establishes cohesion remains unknown. In vitro characterization of Ctf7p as an acetyltransferase led to the model that this activity provides for Ctf7p's essential function [11.Ivanov D. Schleiffer A. Eisenhaber F. Mechtler K. Haering C.H. Nasmyth K. Eco1 is a novel acetyltransferase that can acetylate proteins involved in cohesion.Curr. Biol. 2002; 12: 323-328Abstract Full Text Full Text PDF PubMed Scopus (193) Google Scholar]. However, in vivo Ctf7p substrates have yet to be documented, nor has an in vivo acetyltransferase activity been demonstrated even when Ctf7p is overexpressed [11.Ivanov D. Schleiffer A. Eisenhaber F. Mechtler K. Haering C.H. Nasmyth K. Eco1 is a novel acetyltransferase that can acetylate proteins involved in cohesion.Curr. Biol. 2002; 12: 323-328Abstract Full Text Full Text PDF PubMed Scopus (193) Google Scholar] (A. Brands and R.V. Skibbens, unpublished data). In fact, the effects of acetylation-defective Ctf7p (ctf7ack-) in yeast remain to be rigorously tested, leaving unanswered the critical questions of whether Ctf7p acetyltransferase activity is essential for cell viability and to what extent this activity is required for the establishment of cohesion. Here, we show that yeast strains harboring acetyltransferase-defective alleles [11.Ivanov D. Schleiffer A. Eisenhaber F. Mechtler K. Haering C.H. Nasmyth K. Eco1 is a novel acetyltransferase that can acetylate proteins involved in cohesion.Curr. Biol. 2002; 12: 323-328Abstract Full Text Full Text PDF PubMed Scopus (193) Google Scholar] as the sole source of Ctf7p function exhibit robust growth and high fidelity chromosome transmission.