Poster abstracts

Poster number 77 submitted by Bethany Strunk

Characterization of the essential role of Fap7 in yeast ribosome assembly

Bethany Strunk (Chemical Biology, University of Michigan), Jamie Van Etten (Chemical Biology, University of Michigan), Katrin Karbstein (Department of Chemistry, University of Michigan)

Abstract:
In Saccharomyces cerevisiae, the final cytoplasmic step in the maturation of 40S ribosomes involves cleavage of 20S rRNA to generate the mature 3´ end of 18S rRNA. Several accessory factors are involved in this step, mutations of which lead to accumulation of 20S rRNA in the cytoplasm and failure to produce mature, active ribosomes (1). One such factor is Fap7 an essential protein with ATPase sequence homology believed to act through transient association with the maturing small subunit (2). Conserved amino acids predicted to be involved in ATP hydrolysis are required for Fap7's 18S rRNA processing activity (2). We have demonstrated that Fap7 has ATPase activity. Using a combination of kinetic, fluorescence and proteolysis experiments we have demonstrated that Fap7 dimerizes in the presence of ATP forming an asymmetric dimer. Once both ATP binding sites are filled, ATP is hydrolyzed in a sequential manner. We are currently investigating how this ATPase activity might be used during ribosome assembly and are specifically testing the hypothesis that ATP hydrolysis by Fap7 is used for remodeling of pre-ribosomes. Interestingly, Fap7 has also been implicated in a separate but not necessarily unrelated role, regulation of the Skn7/Pos9 transcriptional response to oxidative stress (3). Fap7 may thus integrate transcriptional and translational response to oxidative stress.

References:
1. Peng et al. Cell. 2003 113(7): 919-33.
2. Granneman et al. Mol Cell Biol. 2005 25(23): 10352-64.
3. Juhnke et al. Mol Microbiol. 2000 35(4): 936-48.
4. Zemp and Kutay. FEBS Letters. 2007 15: 2783-2793.

Keywords: rRNA processing, ribosome assembly, yeast