rhlB, a new Escherichia coli K-12 gene with an RNA helicase-like protein sequence motif, one of at least five such possible genes in a prokaryote.

A newly recognized gene we name rhlB, after RNA helicase-like genes, has been found in the 85-minute region of the Escherichia coli chromosome. This gene encodes protein sequence motifs similar to those known for "D-E-A-D box" gene products. Proteins in this gene family occur in eukaryotes as well as prokaryotes, and, as far as tested, have been found to participate in ATP-dependent RNA helicase or RNA-dependent ATPase activities. The functions of these enzymes are poorly understood. In yeast, mutant phenotypes of various D-E-A-D genes suggest that they function in RNA splicing, processing, or translation. We find that rhlB is necessary for viability only in some genetic backgrounds. Conditional rhlB lethality is not complemented by another E. coli RNA helicase-like gene (srmB). Using primers with homology to consensus sequences in D-E-A-D box proteins, we have recovered DNA fragments amplified from E. coli genomic DNA by polymerase chain reactions. Sequence analysis of these fragments suggests that E. coli possesses at least five RNA helicase-like (rhl) D-E-A-D box genes at widely separated chromosomal locations. The multiplicity of such genes in a prokaryote raises the possibility of important roles for the corresponding class of biologically widespread proteins.