Rid7C, a Member of the YjgF/YER057c/UK114 (Rid) Protein Family, Is a Novel Endoribonuclease That Regulates the Expression of a Specialist RNA Polymerase Involved in Differentiation in Nonomuraea gerenzanensis

The YjgF/YER057c/UK114 (Rid) is a protein family breadth conserved in all domains of life and includes the widely distributed archetypal RidA (YjgF) subfamily and seven other subfamilies (Rid1 to Rid7). Among these subfamilies, RidA is the only family to have been biochemically well characterized and is involved in the deamination of the reactive enamine/imine intermediates. In this study, we have characterized a protein of the Rid7 subfamily, named Rid7C, in Nonomuraea gerenzanensis, an actinomycete that is characterized by the presence of two types of RNA polymerases. This is due to the coexistence in its genome of two RNA polymerase (RNAP) b chain-encoding genes, rpoB(S) (the wild-type rpoB gene) and rpoB(R) (a specialist, mutant-type rpoB gene) that controls A40926 antibiotic production and a wide range of metabolic adaptive behaviors. Here, we found that expression of rpoB(R) is regulated posttranscriptionally by RNA processing in the 59 untranslated region (UTR) of rpoB(R) mRNA and that the endoribonuclease activity of Rid7C is responsible for mRNA processing, thereby overseeing several tracts of morphological and biochemical differentiation. We also provide evidence that Rid7C may be associated with RNase P M1 RNA, although M1 RNA is not required for rpoB(R) mRNA processing in vitro, and that Rid7C endoribonuclease activity is inhibited by A40926, suggesting the existence of a negative feedback loop in A40926 production and a role of the endogenous synthesis of A40926 in the modulation of biochemical differentiation in this microorganism. IMPORTANCE The YjgF/YER057c/UK114 family includes many proteins with diverse functions involved in detoxification, RNA maturation, and control of mRNA translation. We found that Rid7C is an endoribonuclease that is involved in processing of rpoB(R) mRNA, coding for a specialized RNA polymerase beta subunit that oversees morphological differentiation and A40926 antibiotic production in Nonomuraea gerenzanensis. Rid7C-mediated processing promotes rpoB(R) mRNA translation and antibiotic production, while Rid7C endoribonuclease activity is inhibited by A40926, suggesting a role of the endogenous synthesis of A40926 in modulation of biochemical differentiation in this microorganism. Finally, we show that recombinant Rid7C copurified with M1 RNA (the RNA subunit of RNase P) from Escherichia coli extract, suggesting a functional interaction between Rid7C and M1 RNA activities.