Rhs elements of Escherichia coli: a family of genetic composites each encoding a large mosaic protein.
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.
Hill
C W
CW
Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, Hershey 17033.
Sandt
C H
CH
Vlazny
D A
DA
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial