Saccharomyces cerevisiae Pta1 is a component of the cleavage/polyadenylation 
factor (CPF) 3'-end processing complex and functions in pre-mRNA cleavage, 
poly(A) addition, and transcription termination. In this study, we investigated 
the role of the N-terminal region of Pta1 in transcription and processing. We 
report that a deletion of the first 75 amino acids (pta1-Delta75) causes 
thermosensitive growth, while the deletion of an additional 25 amino acids is 
lethal. The pta1-Delta75 mutant is defective for snoRNA termination, RNA 
polymerase II C-terminal domain Ser5-P dephosphorylation, and gene looping but 
is fully functional for mRNA 3'-end processing. Furthermore, different regions 
of Pta1 interact with the CPF subunits Ssu72, Pti1, and Ysh1, supporting the 
idea that Pta1 acts as a scaffold to organize CPF. The first 300 amino acids of 
Pta1 are sufficient for interactions with Ssu72, which is needed for pre-mRNA 
cleavage. By the degron-mediated depletion of Pta1, we show that the removal of 
this essential region leads to a loss of Ssu72, yet surprisingly, in vitro 
cleavage and polyadenylation remain efficient. In addition, a fragment 
containing amino acids 1 to 300 suppresses 3'-end processing in wild-type 
extracts. These findings suggest that the amino terminus of Pta1 has an 
inhibitory effect and that this effect can be neutralized through the 
interaction with Ssu72.