Investigation of the thermal unfolding of secondary and tertiary structure in E. coli tRNAfMet by high-resolution nmr

✍ Scribed by K. Lim Wong; Yeng P. Wong; David R. Kearns

• Publisher: Wiley (John Wiley & Sons)
• Year: 1975
• Tongue: English
• Weight: 780 KB
• Volume: 14
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1975.360140407

✦ Synopsis

Abstract

The high‐resolution (300 MHz) proton nmr spectrum of E. coli tRNA^fMet^ has been examined in 0.17__M__ NaCl, with and without Mg^2+^, and at various temperatures. In light of recent studies of other E. coli tRNA and fragments of tRNA^fMet^, some low field (11–15 ppm) resonances previously assigned to secondary structure base pairs are reassigned to a tertiary structure A~14~–S^4^U~8~ base pair and a protected uridine residue in the anticodon loop. These two resonances and other low field resonances which are assigned to secondary structure base pairs are used to monitor the thermal unfolding of the molecule. In the absence of Mg^2+^ the tertiary structure base pair is present only to ∼45°C, but in the presence of Mg^2+^ it remains until at least 70°C. Analysis of the temperature dependence of other low field resonances indicates that the melting of the dihydrouridine stem occurs more or less simultaneously with the loss of tertiary structure. The observation of the resonance from the A~14~–S^4^U~8~ base pair proves that tertiary structure is present in this molecule below 40°C, even in the absence of Mg^2+^.