Characterization of RNase in Mycoplasma genitalium and study of its possible role in tRNA processing

Exoribonucleases degrade RNA and are important in RNA metabolism and gene expression. Mycoplasma genitalium, a bacterium with the smallest genome known, has only one identified exoribonuclease, RNase R (MgR). In this work RNA degradation properties of purified MgR were examined. As observed in Escherichia coli RNase R (EcR) studies, MgR degrades poly(A), rRNA, and oligoribonucleotides in 3'--->5' direction, though its substrate specificity and optimal activity requirements vary. Interestingly, MgR is sensitive to 2-O-methylation stopping downstream of such modifications in native rRNA and synthetic oligoribonucleotides. MgR removes the 3' trailer sequence from a tRNA precursor of M. genitalium and generates products equal to the mature tRNA, demonstrating a role of MgR in tRNA maturation. The 3' terminal CCA sequence and the acceptor stem of tRNA play a role in determining the formation of such products by MgR. These results suggest multiple functions of RNase R in RNA metabolism in Mycoplasma.