To assess the evolutionary conservation of RNA processing pathways in Aquifex aeolicus, we characterized the products of rRNA and tRNA processing that originated from polycistronic transcripts encoded by the A. aeolicus tufA2 and rRNA operons. We found that, similar to its Escherichia coli counterpart, A. aeolicus RNase E/G is involved in rRNA processing and maturation of tRNAs, thus indicating that RNA processing pathways in E coli and A. aeolicus include common steps and some of them are dependent on RNase E/G. Moreover, although recent biochemical approaches failed to detect an RNase P-like activity in A. aeolicus, our results suggest that such an activity exists in this organism. Accordingly, we show that this activity requires the presence of an RNA component. and magnesium ions in order to be detectable in vitro and therefore shares common properties with bacteria] RNase P. (c) 2007 Elsevier Inc. All rights reserved.