Cef1p is a component of the Prp19p-associated complex and essential for pre-mRNA splicing

The Prp19p protein of the budding yeast Saccharomyces cerevisiae is an esse ntial splicing factor and is associated with the spliceosome during the spl icing reaction. We have previously shown that Prp19p is not tightly associa ted with small nuclear ribonucleoprotein particles but is associated with a protein complex consisting of at least eight protein components. By sequen cing components of the affinity-purified complex, we have identified Cef1p as a component of the Prp19p-associated complex, Ntc85p, Cef1p could direct ly interact with Prp19p and was required for pre-mRNA splicing both in vivo and in vitro. The c-Myb DNA binding motif at the amino terminus of Cef1p w as required for cellular growth but not for interaction of Cef1p with Prp19 p or Cef1p self-interaction. We have identified a small region of 30 amino acid residues near the carboxyl terminus required for both cell viability a nd protein-protein interactions. Cef1p was associated with the spliceosome in the same manner as Prp19p, i.e. concomitant with or immediately after di ssociation of U4, The anti-Cef1p antibody inhibited binding to the spliceos ome of Cef1p, Prp19p, and at least three other components of the Prp19p-ass ociated complex, suggesting that the Prp19p-associated complex is likely as sociated with the spliceosome and functions as an integral complex.