Deletion of the nuclear exosome component RRP6 leads to continued accumulation of the histone mRNA HTB1 in S-phase of the cell cycle in Saccharomyces cerevisiae.

The nuclear exosome, a macromolecular complex of 3' to 5' exonucleases, is required for the post-transcriptional processing of a variety of RNAs including rRNAs and snoRNAs. Additionally, this complex forms part of a nuclear surveillance network where it acts to degrade any aberrantly processed mRNAs in the nucleus. The exosome complex has been implicated in the biogenesis pathway of general messenger RNAs through its interaction with the 3'-end processing machinery. During the cell cycle, yeast histone mRNAs accumulate in the S-phase and are rapidly degraded as cells enter the G2-phase. To determine if the exosome contributes to the cyclic turnover of yeast histone mRNAs, we examined the pattern of accumulation of 'HTB1' mRNA during the cell cycle in a deletion strain of 'RRP6', a component of the nuclear exosome. Our results show that cells lacking Rrp6p continue to accumulate HTB1 mRNA as the cell cycle proceeds. This continued accumulation appears to result from a delay in exit from S-phase in rrp6 cells. The accumulation of HTB1 mRNA in rrp6 cells is influenced by the interaction of the nuclear exosome with the 3'-end processing machinery although there is no evidence for differential regulation of histone mRNA 3'-end processing during the yeast cell cycle.