Genetic analysis of a structural motif within the conserved 530 stem-loop of Escherichia coli 16S rRNA

초록

The 530 stem-loop is a 46 nucleotide stem-loop structure found in all small-subunit ribosornal RNAs. Phylogenetic and mutational studies by others suggest the requirement for Watson-Crick interactions between the nucleotides 505-507 and 524-526 (530 pseudoknot), which are highly conserved. To examine the nature and functional significance of these interactions, a random mutagenesis experiment was conducted in which the nucleotides in the proposed pseudoknot were simultaneously Mutated and functional mutants were selected and analyzed. Genetic analysis revealed that the particular nucleotide present at each position except 524 was not exclusively critical to the selection of functional mutants. It also indicated that base-pairing interactions between the positions 505-507 and 524526 were required for ribosornal function, and much weaker base-pairing interactions than those of the wild-type also allowed high ribosomal function. Our results support the hypothesis that the 530 pseudoknot structure may undergo a "conformational switch" between folded and unfolded states during certain stages of the protein synthesis process by interacting with other ligands present in its environment.

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