The 7SL RNA of eukaryotes is the essential component of the signal recognition particle. A comparative analysis of the 7SL RNA shows that an extensive sequence homology exists with 5S ribosomal RNA but not with the 6S RNA of E. coli. Nevertheless, the analysis of the secondary structures of 7SL and 6S RNA shows that both share a common structural feature. It is therefore possible that also the bacterial 6S RNA is involved in the first step of the secretion process.