The general transcription factor TFIIB plays a central role in preinitiation 
complex (PIC) assembly and the recruitment of RNA polymerase II (RNA pol II) to 
the promoter. Recent studies have revealed that TFIIB engages in contact with 
the transcription termination region and also with complexes that are involved 
in 3' end processing and/or termination. Here we report that TFIIB can be 
phosphorylated within the N terminus at serine 65 in vivo and that the 
phosphorylated form of TFIIB is present within (PICs). Surprisingly, TFIIB 
serine 65 phosphorylation is required after the phosphorylation of serine 5 of 
RNA pol II C-terminal domain (CTD) has occurred, but before productive 
transcription initiation begins. We show that phosphorylation of TFIIB at serine 
65 regulates the interaction between TFIIB and the CstF-64 component of the CstF 
3' cleavage and polyadenylation complex. This directs the recruitment of CstF 
(cleavage stimulatory factor) to the terminator and also the recruitment of the 
CstF and CPSF (cleavage and polyadenylation specific factor) complexes to the 
promoter. Our results reveal that phosphorylation of TFIIB is a critical event 
in transcription that links the gene promoter and terminator and triggers 
initiation by RNA pol II.