A novel interaction between the 5′-untranslated region of eukaryotic messenger RNAs and non-contiguous sequences in the 18 S ribosomal RNA is proposed. The small ribosomal RNA contains, at its 3′-terminus, a heavily conserved hairpin structure. It is suggested that mRNA 5′-leader sequence stabilises this structure by interacting with other conserved nucleotides which flank it. Sequences closely related to the required sequence (A—U—C—C—A—C—C) occur quite commonly in eukaryotic mRNAs and are often found immediately upstream from the AUG-codon. This interaction may have a role in the events which lead up to the initiation of protein synthesis.
