UNCG TETRALOOPS IN SHORT OLIGORIBONUCLEOTIDES REVEAL HIGH THERMODYNAMIC STABILITY AND UNUSUAL STRUCTURAL-PROPERTIES IN AQUEOUS-PHASE AS CONFIRMED BY OPTICAL AND NMR SPECTROSCOPIES

UNCG tetraloops (N = U, A, C, G) (the most frequently found tetraloops in 16S rRNAs) studied in very short hairpins formed in octaribonucleo tides with only two closing G C base pairs in their stems reveal high thermodynamic stability (T-M approximate to 50 degrees C) in aqueous s olutions, On the basis of the experimental results (UV absorption, vib rational and NMR spectra), the unusual high stability of these hairpin s is correlated to the particular structural features of the nucleotid es involved in these tetraloops. As a consequence of our analyses, we can now postulate that all the UNCG tetraloops possess common overall structural features which are independent of the stem length and the n ature of the base (N) located in the second position of the loop. (C) 1997 Elsevier Science B.V.