Abstract: Yeast Pta1 is a component of the 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 deletion of the first 75 amino acids (pta1-Delta75) causes thermosensitive growth while deletion of an additional 25 amino acids is lethal. The pta1-Delta75 mutant is defective for snoRNA termination, RNAP II CTD 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 interaction with Ssu72, which is needed for pre-mRNA cleavage. By degron-mediated depletion of Pta1, we show that removal of this essential region leads to loss of Ssu72, yet surprisingly, in vitro cleavage and polyadenylation remain efficient. In addition, a fragment containing amino acids 1-300 suppresses 3' end processing in wild-type extract. These findings suggest that the amino terminus of Pta1 has an inhibitory effect and this effect can be neutralized through the interaction with Ssu72.