“…Other groups have previously noted numerous twohybrid interactions between Cef1p, Syf1p, Clf1p, Ntc30p/ Isy1p, andNtc20p (Ben-Yehuda et al+, 1998, 2000b;Dix et al+, 1998;Russell et al+, 2000), although it has not been appreciated that these interactions occur within the context of a stable complex+ Although we have not yet placed Ntc30p/Isy1p or Ntc20p within the complex, we have made significant progress in mapping protein interactions between identified and previously unidentified Ntc components+ Interestingly, we have been unable to detect an interaction between Ntc30p/Isy1p and Cef1p that was reported by Ben-Yehuda et al+ (2000b)+ Such an interaction was also not detected by far western analysis (Tsai et al+, 1999;Chen et al+, 2001)+ While our paper was under revision, complementary conclusions regarding the identity of Ntc77p as Clf1p and Ntc90p as Sylf1p were published by Chen et al+ (2002)+ These authors also determined that Clf1p and Syf1p interacted with Cef1p, Ntc20p, and Isy1p (Ntc30p) by two-hybrid analysis+ Of significance to understanding Cdc5p/Cef1p function was our finding that a mutation in PRP19 led to loss of Cef1p+ This indicates that Cef1p/Cdc5p function depends on its interaction with Prp19p+ In light of this finding, although a number of reports have suggested a role for hCDC5 in transcriptional regulation (Hirayama & Shinozaki, 1996;Bernstein & Coughlin, 1997Groenen et al+, 1998), it is likely that Cdc5p/Cef1p is involved primarily in pre-mRNA processing, as no transcriptional function has been attributed to Prp19p+…”