Kirsebom, L. A. | bioRxiv Science

bioRxiv2026

The mycobacterial selenocysteine machinery: presence and expression

The Mycobacterium genus includes more than 190 species that occupies diverse ecological niches. Some are nonpathogenic and environmental, whereas others cause severe diseases both in humans and animals, e.g. tuberculosis (TB) and leprosy. SelenoCysteine (SeC) is present in all three domains of life. Here we report the presence of the SeC-machinery (selA, selB, selC and selD) genes and selenoprotein (fdhA) genes in roughly 40% of 244 mycobacterial genomes. Their presence is distributed evenly among slow and rapid growing mycobacteria and our data indicate that they were acquired through horizontal gene transfer. Some mycobacteria however lost these genes during the evolution of the genus. We provide RNA-Seq data showing transcript levels of the SeC-machinery genes and fdhA in different mycobacteria grown under different conditions. Finally, we suggest that selC (the tRNASeC gene), positioned immediately upstream of selA-selB, is involved in the regulation of the expression of the SeC-machinery genes selA-selB. Together our data expand our understanding of selenocysteine metabolism and its evolution within the Mycobacterium genus.

molecular biology↗

bioRxiv2023

Suppression of the E. coli rnpA49 conditionally lethal phenotype via different compensatory mutations

RNase P is an essential enzyme found across all domains of life that is responsible for the 5-end maturation of precursor tRNA transcripts. Since its discovery in the 1970s, 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. In Escherichia coli, the temperature-sensitive rnpA49 mutation in the protein subunit of RNase P has arguably been one of the most well-studied and commonly used mutations for examining the enzymes activity in vivo. Here we report for the first time naturally-occurring temperature-resistant suppressor mutations of E. coli strains carrying the rnpA49 allele. We find that rnpA49 strains can partially compensate the temperature-sensitive defect via gene amplifications of either RNase P subunit (rnpA49 or rnpB) 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 insight into the behavior and complementation of the rnpA49 allele in vivo and provides direction for follow-up studies regarding RNase P regulation and turnover.

evolutionary biology↗