Suppression of theEscherichia coli rnpA49conditionally lethal phenotype by different compensatory mutations

Abstract

RNase P is an essential enzyme found across all domains of life that is responsible for the 5′-end maturation of precursor tRNAs. For decades, numerous studies have sought to elucidate the mechanisms and biochemistry governing RNase P function. However, much remains unknown about the regulation of RNase P expression, the turnover and degradation of the enzyme, and the mechanisms underlying the phenotypes and complementation of specific RNase P mutations, especially in the model bacterium,Escherichia coli. InE. coli, the temperature-sensitive (ts)rnpA49mutation in the protein subunit of RNase P has arguably been one of the most well-studied mutations for examining the enzyme's activity in vivo. Here, we report for the first time naturally occurring temperature-resistant suppressor mutations ofE. colistrains carrying thernpA49allele. We find thatrnpA49strains can partially compensate the ts defect via gene amplifications of either RNase P subunit (rnpA49orrnpB) or by the acquisition of loss-of-function mutations in Lon protease or RNase R. Our results agree with previous plasmid overexpression and gene deletion complementation studies, and importantly suggest the involvement of Lon protease in the degradation and/or regulatory pathway(s) of the mutant protein subunit of RNase P. This work offers novel insights into the behavior and complementation of thernpA49allele in vivo and provides direction for follow-up studies regarding RNase P regulation and turnover inE. coli.