title: Initial stages of the thermal unfolding of yeast phenylalanine transfer RNA as studied by chemical modification: the effect of magnesium.
abstract: The early stages of thermal unfolding of the tertiary structure of yeast tRNAPhe have been followed, in the presence and absence of Mg2+, by measuring changes in the chemical accessibility of the bases uracil and guanine. The reagent used in these studies is 1-cyclohexyl 3-[2-morpholino(4)-ethyl]carbodiimide methotosylate. 32P-labelled tRNA was used so that the points of modification could be examined with ribonuclease digestion and established fingerprinting techniques. Two regions of protection of Mg2+ have been found. One is within the oligonucleotide U8-A-m2G10 and the other is in the vicinity of residue U-59. The tertiary interactions and the D stem are the most readily melted parts of the teritary structure. In the absence of Mg2+ the region of U-59 is the first part of the tertiary structure to become accessible to the reagent. This is closely followed by the opening up of the 'wobble' G-U base pair in the aminoacyl stem. Most of the triple interactions in the augmented D helix are also disrupted early in the melting. The region of intricate interactions between the invariant G-G part of the D loop and the T-psi-C-G loop contains the most stable set of tertitary structure interactions.
mesh_terms: D001483:Base Sequence; D002234:Carbodiimides; D008274:Magnesium; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009843:Oligoribonucleotides / Q000032:analysis; D010649:Phenylalanine; D012343:RNA, Transfer; D006163:Ribonuclease T1; D012441:Saccharomyces cerevisiae; D013696:Temperature
chemical_list: D002234:Carbodiimides; D009843:Oligoribonucleotides; D010649:Phenylalanine; D012343:RNA, Transfer; D006163:Ribonuclease T1; D008274:Magnesium