A general secondary-structure model for procaryotic and eucaryotic RNAs from the small ribosomal subunits.

A consensus on the folding of the Escherichia coli 16-S ribosomal RNA is emerging and several complete nucleotide sequences of small ribosomal subunit RNAs, covering diverse types of organisms and organelles, are now available. We therefore investigated the extent of both nucleotide sequence and secondary structure conservation that may exist between the E. coli 16-S RNA and other ribosomal RNAs. All the RNA molecules examined could be folded into secondary structure schemes that illustrated remarkable preservation of many structural motifs as well as striking nucleotide sequence conservation compared with the E. coli molecule. This study presents a unitary scheme for the structural organization of the small ribosomal subunit RNAs. The evolutionary constraints on both primary and secondary structures most likely reveal the basic role of some restricted RNA regions in the function of the ribosome.