Abstract

The Small Subunit Processome is a metastable complex that is thought to represent an early checkpoint in the ribosomal small subunit (SSU) assembly pathway. Progression of the SSU Processome towards a mature state involves dynamic rearrangements of RNAs and proteins, but what drives this progression is not known. Previous studies have suggested that the methyltransferase Bud23 acts during SSU Processome progression. Here, we carried out a comprehensive genetic screen that identified bypass suppressors of bud23Δ and link Bud23 to a network of physical interactions that stabilize the SSU Processome. Moreover, two of these factors, the RNA helicase Dhr1 and the EF-Tu-like GTPase Bms1, are thought to facilitate crucial structural rearrangements. We propose a model in which Bud23 binding to the 3’-domain promotes the release of factors surrounding its binding site to drive rearrangements during the progression of the SSU Processome.