The stable RNAs, whose sequences are homologous to 10Sa RNA of Escherichia coli, have been isolated from Mycoplasma capricolum and Bacillus subtilis, both belonging to the Gram-positive bacterial group. The total nucleotide sequences of the RNAs have been determined by partial RNA sequencing and DNA sequencing of their genes. A comparison of the sequences, together with those of other bacterial 10Sa RNAs so far known, has shown that the 5'- and 3'-end sequences are well conserved among species, while the central parts reveal little homologies. Unexpectedly, the conserved 5'- and 3'-regions can be folded in a common tRNA-like structure containing an amino acid-acceptor stem and a T phi C-stem/loop. The 3'-terminal CCA sequence of B.subtilis 10Sa RNA is not encoded on the DNA, but is added after transcription. Furthermore, the RNA is aminoacylatable with alanine in vitro, and binds to the 70S ribosome in vivo.