Rate of transcription elongation and sequence-specific pausing by RNA polymerase I directly influence ribosomal RNA processing.

ABSTRACT: One of the first steps in ribosome biogenesis is transcription of the ribosomal DNA (rDNA) by RNA polymerase I (Pol I). Processing of the resultant ribosomal RNA (rRNA) begins co-transcriptionally and perturbation of Pol I transcription elongation results in defective rRNA processing. Mechanistic insight regarding the link between transcription elongation and ribosome assembly is lacking due to limited in vivo methods to assay Pol I transcription. Here, we use native elongating transcript sequencing (NET-seq) with a strain of Saccharomyces cerevisiae containing a point mutation in Pol I, rpa190-F1205H, which results in impaired rRNA processing and ribosome assembly. We previously demonstrated that this mutation caused a mild reduction in the transcription elongation rate of Pol I in vitro, however, transcription elongation by the mutant has not been characterized in vivo. Here, our findings demonstrate that the mutant Pol I has an increased pause propensity during processive transcription elongation both in vitro and in vivo. NET-seq reveals that rpa190-F1205H Pol I displays alternative pause site preferences in vivo. Specifically, the mutant is sensitized to A/G residues in the RNA:DNA hybrid and at the last incorporated nucleotide position. Furthermore, both NET-seq and EM analysis of Miller chromatin spreads reveal pileups of rpa190-F1205H Pol I throughout the rDNA, particularly at the 5' end of the 35S gene. This combination of in vitro and in vivo analyses of the Pol I mutant provides novel insights into Pol I elongation properties and indicates how these properties are crucial for efficient co-transcriptional rRNA processing and ribosome assembly.

SUBMITTER: Huffines AK 

PROVIDER: S-EPMC9768379 | biostudies-literature | 2022 Nov

REPOSITORIES: biostudies-literature