Abstract
Mycoplasmas are pathogens causing infectious diseases in various animals, including humans. They are also common contaminants of cell culture. Although it is suggested that mycoplasmas alter nucleic acid metabolism of host cells through their nucleases, the actual impact of the nucleases on host cell RNAs is unknown. Here we report that Mycoplasma hyorhinis, a common laboratory contaminant species, promotes cleavage of host cell transfer RNAs (tRNAs) through a membrane-associated nuclease. When infected by M. hyorhinis, scraping of cells as well as cell lysis induced a marked cleavage of host RNAs. Further analysis suggested that the protein encoded by the membrane nuclease A (mnuA) gene is responsible for the host RNA cleavage. MnuA protein demonstrates DNase and RNase activities dependent on Ca2+/Mg2+ ions. Purified MnuA protein acts as an atypical sugar non-specific nuclease: while it possesses broad DNase activities, its RNase activity is highly specific to tRNAs in live cells. Mutational analysis shows that the nuclease activity is mediated by a domain which is highly similar to DNase I. Furthermore, M. hyorhinis promoted cleavage of host tRNAs under amino acid deprivation, suggesting that M. hyorhinis infection may alter RNA metabolism in host cells under certain physiological stress. As mnuA genes are conserved in various mycoplasma species, our findings provide novel insights into the effects of MnuA nucleases on host cell RNAs under mycoplasma infection.