Universal structural features of prokaryotic and eukaryotic ribosomal 5S RNA derived from comparative analysis of their sequences.

An extensive comparative analysis of more than fifty available sequences of ribosomal 5S RNA has been made. Both for prokaryotic and eukaryotic 5S RNA a generalized secondary structure is presented which is similar to that suggested by Nishikawa and Takemura modified in few positions only. Both generalized secondary structures contain five main helical regions and a high base-pairing content of about 65 +/- 5%. The general structural architecture of prokaryotic and eukaryotic 5S RNA molecules appears to be very similar with minor modifications within particular subgroups of organisms. Conserved and semiconserved nucleotides are accumulated in the single stranded parts of 5S RNA. Functional importance was suggested for some of these regions; other short conserved nucleotide stretches may be involved in the folding of 5S RNA molecules. In particular, we propose a tertiary base-pairing interaction between the universal invariant GUA sequence (positions 76-78 and 75-77 in prokaryotic and eukaryotic 5S RNA, respectively) and the complementary conserved CPuU sequence (positions 38-40 and 36-38) in a parallel manner. A molecular model of the 5S RNA of human KB cells was constructed, which verifies the proposed tertiary interaction, probably stabilizing the two neighboured helices E and D and a stacking arrangement of the bases in the sequence positions 67-108 (and 70-106) in eukaryotic (and prokaryotic) 5S RNAs, respectively.