Читать книгу Chemistry and Biology of Non-canonical Nucleic Acids - Naoki Sugimoto - Страница 37

T-loop motif is well-observed motif in the loop–loop interaction regions, which have been identified in a variety of RNAs [30]. T-loop motif generally consists of five consecutive nucleotides assuming a compact U-turn-like loop structure, in which the first and the fifth nucleobases form a base pair irrespective of whether it is canonical Watson–Crick or unusual one. When the T-loop motif is involved in the loop–loop interaction, the fourth and fifth nucleobases in the T-loop sandwich an extra nucleobase, which is derived from separated loop region, to make continuous base stacks. The sandwiched nucleobase usually interacts with the second nucleobase of the T-loop through hydrogen bonding [30]. In crystal structure of phenylalanyl-tRNA derived from Saccharomyces cerevisiae, in which T-loop motif was originally discovered, UUCGA loop of pentanucleotides accommodates guanine nucleobase from different tRNA loop region to form stable tertiary interaction (Figure 2.14).