The RNase P protein gene ( rnpA ) completely overlaps the rpmH gene (encoding ribosomal protein L34) out of frame in the thermophilic bacterium Thermus thermophilus . This results in the synthesis of an extended RNase P protein (C5) of 163 aa and, by inference, of 240 aa in the related strain Thermus filiformis . Start codons of rnpA and rpmH , apparently governed by the same ribosome binding site, are separated by only 4 nt, which suggests a regulatory linkage between L34 and C5 translation and, accordingly, between ribosome and RNase P biosynthesis. Within the sequence encoding the N-terminal extensions and downstream of rpmH , several Thermus species exhibit in-frame deletions/insertions, suggesting relaxed constraints for sequence conservation in this region. Roughly the N-terminal third of T. thermophilus C5 was further shown to be dispensable for RNase P function in vitro by using a precursor tRNA ^Gly substrate from the same organism. Taken together, these data reveal a mode of gene expression that is to our knowledge unprecedented in bacteria.