G-ribo motif favors the formation of pseudoknots in ribosomal RNA

Analysis of the pseudoknots existing in the ribosomal RNA showed that four of them are formed with the help of G-ribo, a recently identified RNA recurrent motif. The analysis of these pseudoknots revealed two major aspects in the G-ribo motif structure, which together provide the structural context favoring the formation of two different types of pseudoknots. The first aspect pertains to a particular side-by-side juxtaposition of two double helices that facilitates switches of the polynucleotide chain between different strands. The second aspect deals with the presence of an adenosine at a specific place where it can stabilize a particular arrangement of two quasicoaxial helices required for the pseudoknot formation. Additional analysis shows that the latter aspect is also present in other pseudoknots not related to the G-ribo motif or the ribosome, and thus represents a general structural element favoring the formation of pseudoknots.