Nucleic Acids Research, 1981, Vol. 9, No. 16 4081-4086
© 1981
MOLECULAR BIOLOGY |
A hydrogen exchange study of Escherichia coli 5S RNA
Centre de Biophysique Moléculaire, 1A, avenue de la Recherche Scientifique 45045 Orléans Cédex, France Institut für Biochemie, Freie Universität Berlin Thiel Allee 69-73, D-1000 Berlin 33 Dahlem, GFR
Received June 30, 1981. Using the tritium Sephadex method, the number of exchangeable protons in E. coli. 5S RNA and the kinetics of their exchange reactions have been measured at two different Mg++ concentrations (102 M and 103 M). A quantitative analysis of these results indicates the presence of two classes of protons exchanging with very different rates. The protons of the slow class, not seen in linear molecules of double helical RNA, exchange with a half-time of 0.6 hour and their exchange kinetics are independent of Mg++ concentration. Reduction of the Mg++ concentration from 102 to 103 M, however, results in a decrease in the number of these exchangeable protons from 26 to 19. Neither the total number, nor the exchange kinetics of the fast protons are affected by this change in Mg++ concentration. Comparison of these results with those previously obtained with tRNA, suggests the presence of a Mg++ dependent tertiary structure in 5S RNA. The number of exchangeable protons obtained from extrapolation of the exchange curves (120 and 126 respectively for 103 and 102 MMg++ concentration are compared to the calculated number of exchangeable protonspredicted by previous proposed structural models for E.coli 5S RNA.