title: Stability of non-Watson-Crick G-A/A-G base pair in synthetic DNA and RNA oligonucleotides.
abstract: A non-Watson-Crick G-A/A-G base pair is found in SECIS (selenocysteine-insertion sequence) element in the 3'-untranslated region of Se-protein mRNAs and in the functional site of the hammerhead ribozyme. We studied the stability of G-A/A-G base pair (bold) in 17mer GT(U)GACGGAAACCGGAAC synthetic DNA and RNA oligonucleotides by thermal melting experiments and gel electrophoresis. The measured Tm value of DNA oligonucleotide having G-A/A-G pair showed an intermediate value (58 degrees C) between that of Watson-Crick G-C/C-G base pair (75 degrees C) and that of G-G/A-A of non-base-pair (40 degrees C). Similar thermal melting patterns were obtained with RNA oligonucleotides. This result indicates that the secondary structure of oligonucleotide having G-A/A-G base pair is looser than that of the G-C type Watson-Crick base pair. In the comparison between RNA and DNA having G-A/A-G base pair, the Tm value of the RNA oligonucleotide was 11 degrees C lower than that of DNA, indicating that DNA has a more rigid structure than RNA. The stained pattern of oligonucleotide on polyacrylamide gel clarified that the mobility of the DNA oligonucleotide G-A/A-G base pair changed according to the urea concentration from the rigid state (near the mobility of G-C/C-G oligonucleotide) in the absence of urea to the random state (near the mobility of G-G/A-A oligonucleotide) in 7 M urea. However, the RNA oligonucleotide with G-A/A-G pair moved at an intermediate mobility between that of oligonucleotide with G-C/C-G and of the oligonucleotide with G-G/A-A, and the mobility pattern did not depend on urea concentration. Thus, DNA and RNA oligonucleotides with the G-A/A-G base pair showed a pattern indicating an intermediate structure between the rigid Watson-Crick base pair and the random structure of non-base pair. RNA with G-A/A-G base pair has the intermediate structure not influenced by urea concentration. Finally, this study indicated that the intermediate rigidity imparted by Non-Watson-Crick base pair in SECIS element plays an important role in the selenocysteine expression by UGA codon.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ito
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Sone
authors.forename: Takaharu
authors.initials: T
authors.lastname: Mizutani
mesh_terms: D020029:Base Pairing; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D009841:Oligonucleotides / Q000138:chemical synthesis* / Q000737:chemistry; D012313:RNA / Q000737:chemistry* / Q000235:genetics; D017279:Selenocysteine / Q000737:chemistry / Q000235:genetics; D013329:Structure-Activity Relationship; D014508:Urea / Q000737:chemistry
chemical_list: D009841:Oligonucleotides; D017279:Selenocysteine; D012313:RNA; D014508:Urea; D004247:DNA