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

Mol Cell Biol. 2009 Apr;29(8):2296-307. doi: 10.1128/MCB.01514-08. Epub 2009 Feb 2.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Carrier Proteins / physiology*
  • Mutant Proteins
  • Phosphoprotein Phosphatases
  • Polyadenylation
  • RNA 3' End Processing*
  • RNA Precursors / metabolism*
  • RNA, Small Nucleolar / genetics*
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / physiology*
  • Sequence Deletion
  • Transcription, Genetic*
  • mRNA Cleavage and Polyadenylation Factors / chemistry
  • mRNA Cleavage and Polyadenylation Factors / physiology*

Substances

  • Carrier Proteins
  • Mutant Proteins
  • PTA1 protein, S cerevisiae
  • RNA Precursors
  • RNA, Small Nucleolar
  • SSU72 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • mRNA Cleavage and Polyadenylation Factors
  • Phosphoprotein Phosphatases