[Destruction of mRNA poly-A sequences by polynucleotide phosphorylase in rat liver microsomes]

A possible role of polynucleotide Phosphorylase (PNPase) in the destruction of poly-A fragments located at the 3'-OH end of mRNA from rat liver polyribosomes was studied. Using hybridization of mRNP particles and mRNA with poly-U Sepharose 4B, it was found that polyribosomal PNPase in vitro destroys the poly-A sequences of approximately 25% of poly-A+ mRNA during the first minutes of incubation at a high rate. The destruction of the poly-A fragment of mRNA by PNPase is incomplete, since part of it is presumably protected by proteins firmly bound to the poly-A sequences of mRNA.