Processing of the 17-S Escherichia coli precursor RNA in the 27-S pre-ribosomal particle.

An RNase activity probably involved in the maturation of 16-S pre-ribosomal RNA in Escherichia coli has been partially purified from crude cell extracts. When 27-S ribosome precursor particles are incubated with this enzyme preparation in vitro, their 17-S RNA is converted to a product with the same electrophoretic mobility as mature 16-S rRNA. Fingerprint analysis of this product shows that it contains the 3'-OH but not the 5'-P terminus of mature 16-S rRNA. Generation of the normal 5'-P terminus seems to require a factor present in cell extracts since incubation of the 27-S precursor particle in an extract obtained after centrifugation at 30 000 x g causes conversion of the 17-S RNA to a 16-S species containing both termini of mature 16-S rRNA. Preliminary experiments suggest that correct maturation of the 5' end of the 17-S precursor RNA requires a system in which protein synthesis can take place.