The essential N terminus of the Pta1 scaffold protein is required for snoRNA transcription termination and Ssu72 function but is dispensable for pre-mRNA 3'-end processing.

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.
Mesh Terms:
Carrier Proteins, Mutant Proteins, Phosphoprotein Phosphatases, Polyadenylation, RNA 3' End Processing, RNA Precursors, RNA, Small Nucleolar, Saccharomyces cerevisiae Proteins, Sequence Deletion, Transcription, Genetic, mRNA Cleavage and Polyadenylation Factors
Mol. Cell. Biol.
Date: Apr. 01, 2009
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