Poster abstracts

Poster number 69 submitted by Bethany Strunk

Characterization of the essential role of Fap7 in yeast ribosome assembly

Bethany Strunk (Chemical Biology, University of Michigan), Ramya Krishnan (Chemistry, University of Michigan), Katrin Karbstein (Chemistry, University of Michigan)

Abstract:
Ribosome assembly requires binding and release of accessory proteins from pre-ribosomes. For different accessory factors to stably associate with and dissociate from pre-ribosomal complexes at specific stages, energy must be input during binding or dissociation to alter the free energy of the protein-complex interactions. Fap7 is an accessory factor essential for small subunit (SSU) assembly and has sequence homology to ATPases. Mutations in conserved amino acids predicted to be involved in Fap7’s ATPase activity are essential for growth and ribosome assembly in yeast (1). Previous work has shown that Fap7 interacts directly with the SSU component RpS14 and depletion of Fap7 leads to retention of Rio2, a protein kinase required for 20S processing, in pre-ribosomal complexes (1). Our own experiments indicate that this retention is specific and not simply due to increased levels of 20S rRNA because Nob1, which also binds this intermediate, does not accumulate when Fap7 is depleted. Based on these data, we propose the following model: Rio2 bound to the pre-ribosome inhibits cleavage of the 20S pre-rRNA to produce the mature 18S rRNA. Fap7 binds Rps14 in proximity to Rio2 and uses its ATPase activity to remove Rio2 from pre-ribosomes, either through phosphorylation of Rio2, another protein, rRNA, or through a non-kinase motor-like ATPase activity, allowing continuation of ribosome maturation. We are using a combination of biochemical techniques and in vivo studies to explore Fap7’s essential role in ribosome assembly.

References:
Granneman et al. Mol Cell Biol. 2005 25(23): 10352-64.

Keywords: rRNA processing, ribosome assembly