RhlB

RhlB is a DEAD-box RNA helicase that functions as a component of the bacterial RNA degradosome, a multi-enzyme complex involved in mRNA decay. In Escherichia coli, the core degradosome consists of RNase E, RhlB, polynucleotide phosphorylase (PNPase), and enolase; RhlB associates with RNase E and helps remodel RNA substrates to promote cleavage and exonucleolysis. The protein is cytoplasmic and acts on RNA substrates in conjunction with other degradosome components, contributing to rapid turnover of transcripts and processing of structured RNAs.

RhlB belongs to the DEAD-box family of RNA helicases. It contains the conserved helicase core motifs, including the Q motif, the Walker A (P-loop) motif I, the DEAD motif (motif II), and motif III (SAT), which coordinate ATP binding and hydrolysis with RNA binding and unwinding. The helicase activity enables RhlB to unwind short RNA duplexes, facilitating access for RNase E and other ribonucleases. The directionality of translocation is not the primary descriptor; rather, its activity helps destabilize secondary structures that hinder decay.

RhlB homologs are found in many related bacteria, and the gene is typically designated rhlB in genome annotations. While the degradosome composition varies across species, the role of RhlB as an ATP-dependent RNA remodeling factor linked to RNA decay is conserved. Disruption of rhlB impairs efficient degradation of certain structured RNAs and can affect gene expression responses to environmental changes.