Date of Award

7-13-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Ann Flower

Abstract

The BipA protein belongs to the EF-Tu/EF-G family of translational factors. In addition to intriguing domain similarities to the elongation factor subfamily members, BipA also possesses ribosome-binding capability and GTPase activity that is enhanced by the presence of fully programmed ribosomes. BipA has been shown to be involved in the regulation of a variety of pathways in different bacterial species; these include a role in pathogenicity, oxidative stress, capsule formation, motility, and growth at low temperatures. These two points have led to speculation that BipA may be a novel regulatory protein that affects efficient translation of target genes through direct interaction with the ribosome. The cold-sensitive phenotype of a bipA deletion strain was utilized to isolate and characterize suppressors that were able to grew more robustly than the parent ΔbipA strain at 20°C. We determined that deletion of rluC leads to suppression of the cold-sensitive growth phenotype. The rluC gene encodes a pseudouridine synthase responsible for pseudouridine modification of 23S rRNA at three sites, all located in the peptidyl transferase center. The suppressor effect is specific to rluC as deletion of other rlu genes did not relieve cold sensitivity, and further, more than a single pseudouridine residue is involved as alteration to single sites did not produce suppressors. These results are consistent with the proposed function of BipA as translational regulator that exerts it effect by interaction with the ribosome. To elucidate the physiological function of BipA, we examined its role in colanic acid synthesis and flagella-mediated motility in Escherichia coli K12. We determined that the regulation of flagella-mediate motility by BipA is independent of RcsBCD phosphorelay system and that the effect of BipA on pathways in question is likely mediated by a secondary factor, H-NS.

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