1a4x: Difference between revisions

BACKGROUND: The expression of pyrimidine nucleotide biosynthetic (pyr), genes in Bacillus subtilis is regulated by transcriptional attenuation., The PyrR attenuation protein binds to specific sites in pyr mRNA, allowing, the formation of downstream terminator structures. UMP and, 5-phosphoribosyl-1-pyrophosphate (PRPP), a nucleotide metabolite, are, co-regulators with PyrR. The smallest RNA shown to bind tightly to PyrR is, a 28-30 nucleotide stem-loop that contains a purine-rich bulge and a, putative-GNRA tetraloop. PyrR is also a uracil phosphoribosyltransferase, (UPRTase), although the relationship between enzymatic activity and RNA, recognition is unclear, and the UPRTase activity of PyrR is not, physiologically significant in B. subtilis. Elucidating the role of PyrR, structural motifs in UMP-dependent RNA binding is an important step, towards understanding the mechanism of pyr transcriptional attenuation., RESULTS: The 1.6 A crystal structure of B. subtilis PyrR has been, determined by multiwavelength anomalous diffraction, using a Sm, co-crystal. As expected, the structure of PyrR is homologous to those, proteins of the large type I PRTase structural family; it is most similar, to hypoxanthine-guanine-xanthine PRTase (HGXPRTase). The PyrR dimer, differs from other PRTase dimers, suggesting it may have evolved, specifically for RNA binding. A large, basic, surface at the dimer, interface is an obvious RNA-binding site and uracil specificity is, probably provided by hydrogen bonds from mainchain and sidechain atoms in, the hood subdomain. These models of RNA and UMP binding are consistent, with biological data. CONCLUSIONS: The B. subtilis protein PyrR has, adapted the substrate- and product-binding capacities of a PRTase, probably an HGXPRTase, producing a new regulatory function in which the, substrate and product are co-regulators of transcription termination. The, structure is consistent with the idea that PyrR regulatory function is, independent of catalytic activity, which is likely to be extremely low, under physiological conditions.

1A4X is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Bacillus_subtilis Bacillus subtilis] with SO4 as [http://en.wikipedia.org/wiki/ligand ligand]. Structure known Active Sites: PRA and PRB. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1A4X OCA].  

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