Skin Biopsy Procedures: How and Where to Perform a Proper Biopsy

Abstract

The Escherichia coli Rsd protein binds tightly and specifically tothe RNA polymerase (RNAP) sigma(70) factor. Rsd plays a role in alternativesigma factor-dependent transcription by biasing the competition betweensigma(70) and alternative sigma factors for the available core RNAP.Here, we determined the 2.6 A-resolution X-ray crystal structureof Rsd bound to sigma(70) domain 4 (sigma(70)(4)), the primary determinantfor Rsd binding within sigma(70). The structure reveals that Rsdbinding interferes with the two primary functions of sigma(70)(4),core RNAP binding and promoter -35 element binding. Interestingly,the most highly conserved Rsd residues form a network of interactionsthrough the middle of the Rsd structure that connect the sigma(70)(4)-bindingsurface with three cavities exposed on distant surfaces of Rsd, suggestingfunctional coupling between sigma(70)(4) binding and other bindingsurfaces of Rsd, either for other proteins or for as yet unknownsmall molecule effectors. These results provide a structural basisfor understanding the role of Rsd, as well as its ortholog, AlgQ,a positive regulator of Pseudomonas aeruginosa virulence, in transcriptionregulation.