Poster abstracts
Poster number 14 submitted by Michelle Gibbs
Role of the conserved GTPase BipA in assembly of the 50S subunit of the ribosome
Michelle R. Gibbs (Department of Microbiology and Center for RNA Biology, The Ohio State University), Kyung-Mee Moon (Department of Biochemistry and Molecular Biology, University of British Columbia), Leonard J. Foster (Department of Biochemistry and Molecular Biology, University of British Columbia), Kurt Fredrick (Department of Microbiology and Center for RNA Biology, The Ohio State University)
Abstract:
BipA is a conserved translational GTPase that resembles elongation factor EF-G and 30S assembly factor LepA. Recent evidence from the Flower group suggests that BipA functions in 50S subunit assembly, but the precise role of the factor remains unclear. Here, we use stable isotope labeling of amino acids in culture and mass spectrometry (SILAC / MS) to examine the function of BipA in ribosome biogenesis. During growth at suboptimal temperature, loss of BipA leads to accumulation of immature large subunit particles (~40S) that lack several proteins. These include L2, L14, L16, L17, L19, and L32. Parallel analysis of the control (wild-type) strain shows accumulation of virtually identical intermediate particles, although at much lower levels. These data suggest that BipA acts in some way to destabilize this ~40S intermediate that accumulates in the cold. Loss of BipA causes no apparent defect in 30S subunit assembly. In fact, the proportion of 30S assembly intermediates decreases in the mutant strain, presumably due to an increase in free mature 30S subunits unable to enter the translation pool because they have no functional 50S partner. Notably, LepA and BipA bind similarly to the ribosome, and the GTP hydrolysis activity of each factor depends on the intact 70S ribosome. Based on these observations, we propose that, for each subunit, part of the assembly process occurs in the context of the 70S ribosome.
Keywords: ribosome assembly, GTPase, BipA