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Protein Domain : RNA-binding protein Hfq

Primary Identifier  IPR005001 Type  Family
Short Name  Hfq
description  This entry represents the RNA-binding pleiotropic regulator Hfq, a small, Sm-like protein of bacteria. It helps pair regulatory non-coding RNAs with complementary mRNA target regions. It enhances the elongation of poly(A) tails on mRNA. It appears also to protect RNase E recognition sites (A/U-rich sequences with adjacent stem-loop structures) from cleavage. Being pleiotropic, it differs in some of its activities in different species. Hfq binds the non-coding regulatory RNA DsrA (see Rfam:RF00014) in the few species known to have it: Escherichia coli, Shigella flexneri, Salmonella spp. In Azorhizobium caulinodans, an hfq mutant is unable to express nifA, and Hfq is called NrfA, for nif regulatory factor (see ). The name Hfq reflects phenomenology as a host factor for phage Q-beta RNA replication.The Hfq protein is conserved in a wide range of bacteria and varies in length from 70 to 100 amino acids. In all cases, a conserved Sm motif is located in the N-terminal halves of the molecules. The Hfq protein of E. coli is an 11kDa polypeptide that forms a hexameric ring-shaped structure. Structural studies have suggested that the beta-4 strand in one molecule dimerises with the beta-5 strand of a neighbouring subunit to form the hexamer. These two strands move with a concerted mobility which may explain the stability of the entire structure [].The architecture of the Hfq-RNA complex suggests two, not mutually exclusive, mechanisms by which Hfq might exert its function as modulator of RNA-RNA interactions. First, when Hfq binds single-stranded RNA, the target site is unwound in a circular manner. This would greatly destabilise surrounding RNA structures that are located several nucleotides on either side of the binding site, thereby permitting new RNA-RNA interactions. Secondly, the repetition of identical BPs on the Hfq hexamer implies that the binding surface can accommodate more than just a single RNA target. This would allow simultaneous binding of two RNA strands and could greatly enhance interaction between the strands [].

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