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  • Title: Rhs elements of Escherichia coli: a family of genetic composites each encoding a large mosaic protein.
    Author: Hill CW, Sandt CH, Vlazny DA.
    Journal: Mol Microbiol; 1994 Jun; 12(6):865-71. PubMed ID: 7934896.
    Abstract:
    The Rhs family comprises a set of composite elements found in the chromosomes of many natural Escherichia coli strains. Five Rhs elements occur in strain K-12. The most prominent Rhs component is a giant core open reading frame (core ORF) whose features are suggestive of a cell surface ligand-binding protein. This hypothetical protein contains a peptide motif, xxGxxxRYxYDxxGRL(I or T)xxxx, that is repeated 28 times. A similar repeated motif is found in a Bacillus subtilis wall-associated protein. The Rhs core ORFs consist of two distinct parts: a large N-terminal core that is conserved in all Rhs elements, and a smaller C-terminus that is highly variable. Distinctive G+C contents of Rhs components indicate that the elements have a recent origin outside the E. coli species, and that they are composites assembled from segments with very different evolutionary histories. The Rhs cores fall into three sub-families that are mutually more than 20% divergent. Downstream of the core ORF is a second, much shorter ORF. Like the adjacent core extension, these are highly variable. In most examples, the hypothetical product of this ORF has a candidate signal sequence for transport across the cytoplasmic membrane. Another Rhs component, the 1.3 kb H-rpt, has features typical of insertion sequences. Structures homologous to H-rpt have been detected in other bacterial genera, such as Vibrio and Salmonella, where they are associated with loci that determine O-antigen variation.
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