Poster abstracts

Poster number 85 submitted by Jason Talkish

Disruption of ribosome biosynthesis results in a shift from co- to post-transcriptional pre-rRNA processing and breakdown of the traditional assembly hierarchy

Jason Talkish, Jelena Jakovljevic, Jingyu Zhang, Lan Tang (Department of Biological Sciences, Carnegie Mellon University), John Strahler (Michigan Proteome Consortium, University of Michigan), Philip C. Andrews (Michigan Proteome Consortium, University of Michigan), Janine Maddock (Department of Molecular, Cellular, and Developmental Biology, University of Michigan), John L. Woolford, Jr. (Department of Biological Sciences, Carnegie Mellon University)

Abstract:
In mammals, pre-rRNA processing happens almost exclusively post-transcriptionally. This is not the case in rapidly dividing yeast, as the majority of pre-rRNA is processed co-transcriptionally. The process of ribosome assembly is thought to be driven, in part, by the hierarchical association of assembly factors and r-proteins. It is well established that there are groups of proteins that associate with nascent ribosomes early in assembly, during the middle of assembly, or only at the end of assembly. Here, in the course of studying Drs1, we find that disruption of ribosome assembly results in a significant shift from co- to post-transcriptional pre-rRNA processing and breakdown of the traditional assembly hierarchy. Previously Drs1 was shown to be required for production of 60S subunits and function in 27SB pre-rRNA processing. Here we show that depletion of Drs1 affects earlier steps of pre-rRNA processing and that Drs1 functionally and physically interacts with the Nop7-subcomplex. Most important, we show that depletion of Drs1 and subsequent disruption of ribosome biogenesis causes pre-rRNAs to be processed post-transcriptionally. We describe a previously unreported phenotype, in which late-binding 66S assembly factors associate with early pre-ribosomes containing 35S pre-rRNA. The shift from co- to post-transcriptional pre-rRNA processing, and the ability of late-associating proteins to bind pre-ribosomes very early in assembly drastically changes the current views on the hierarchy of ribosome assembly.

Keywords: ribosome assembly, pre-rRNA processing, co-transcriptional processing