Effects of N2,N2-dimethylguanosine on RNA structure and stability: crystal structure of an RNA duplex with tandem m2 2G:A pairs.

Pallan PS, Kreutz C, Bosio S, Micura R, Egli M
RNA. 2008 14 (10): 2125-35

PMID: 18772248 · PMCID: PMC2553729 · DOI:10.1261/rna.1078508

Methylation of the exocyclic amino group of guanine is a relatively common modification in rRNA and tRNA. Single methylation (N(2)-methylguanosine, m(2)G) is the second most frequently encountered nucleoside analog in Escherichia coli rRNAs. The most prominent case of dual methylation (N(2),N(2)-dimethylguanosine, m(2) (2)G) is found in the majority of eukaryotic tRNAs at base pair m(2) (2)G26:A44. The latter modification eliminates the ability of the N(2) function to donate in hydrogen bonds and alters its pairing behavior, notably vis-à-vis C. Perhaps a less obvious consequence of the N(2),N(2)-dimethyl modification is its role in controlling the pairing modes between G and A. We have determined the crystal structure of a 13-mer RNA duplex with central tandem m(2) (2)G:A pairs. In the structure both pairs adopt an imino-hydrogen bonded, pseudo-Watson-Crick conformation. Thus, the sheared conformation frequently seen in tandem G:A pairs is avoided due to a potential steric clash between an N(2)-methyl group and the major groove edge of A. Additionally, for a series of G:A containing self-complementary RNAs we investigated how methylation affects competitive hairpin versus duplex formation based on UV melting profile analysis.

MeSH Terms (12)

Adenine Base Pairing Base Pair Mismatch Crystallography, X-Ray Guanosine Hydrogen Bonding Methylation Nucleic Acid Conformation RNA RNA Stability Transition Temperature Ultraviolet Rays

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