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BipA is a multi-domain prokaryotic GTPase that associates with the ribosome. Although the exact cellular function of this protein remains elusive, BipA homologs have been implicated in a number of cellular processes including expression of virulence genes, low temperature growth, flagella mediated motility, and other cellular processes associated with stress response. We are utilizing biochemical and biophysical techniques to study the Salmonella typhimurium homolog of BipA in order to better understand its cellular function. Using sucrose density gradients and pelleting assays we have shown that BipA interacts with the ribosome in vivo, and that the GTP bound state of the protein associates with the ribosome in vitro. We have also determined that association with 70S ribosomes significantly stimulates the GTPase activity of the protein. The C-terminal region of the protein has been found to mediate the stimulatory effect of the ribosome on BipA hydrolysis. As is the case with other multidomain switch proteins, intramolecular interactions play a role in regulating the GTPase activities of BipA. We have also employed competition assays with antibiotics to identify the general location on the ribosome occupied by BipA. Together, these studies provide us with some initial details as to the nature of the BipA-ribosome interaction. [ABSTRACT FROM AUTHOR]