Exposure of Bacillus subtilisto mercury induces accumulation of shorter tRNA super(Cys) species

RNA processing is an essential pathway in the regulation of genetic expression in the cell. In this work, Bacillus subtiliswas used to understand the effects of mercury on the mechanism of tRNA metabolism. The CVAAS (cold vapor atomic absorption spectroscopy) method revealed that from the addition of HgCl sub(2) (0.75 mu g ml super(-1)) during the bacterial exponential phase, ca.48% of the added mercury was taken up by the cells. This led to an immediate reduction in the rate of cell division. During this response, we observed accumulation of species shorter than mature tRNA super(Cys) over a 10 h period. We did not observe this accumulation for another five tRNAs analyzed. tRNA processing is largely dependent on RNase R and PNPase in B. subtilis. Thus, when the exonuclease PNPase was absent, we found that the shorter tRNA super(Cys) species increased and mature tRNA super(Cys) decreased after mercury addition, but this proportion changed during the time analyzed. However, in the absence of RNase R and PNPase the accumulation of the shorter tRNA super(Cys) was more pronounced and the mature form was not recovered. In the single rnrmutant strain the shorter tRNA super(Cys) was not observed. All together, we provide in vivoevidence that PNPase and RNase R are indispensable in controlling tRNA super(Cys) quality in the presence of mercury.