[A thermodynamic approach to the study of the structural organization of 5S RNA from Escherichia coli ribosomes. 1. Analysis of scanned microcalorimetry data].

Melting of the 5S RNA from E. coli ribosomes has been studied by differential scanning microcalorimetry. It has been shown that: (1) heat capacity temperature functions of the "native" and A-forms of the 5S RNA coincide in all the conditions studied; (2) heat capacity temperature functions of the B-form of the 5S RNA differ in a low-temperature region from the heat capacity functions of the A-form, the complete melting enthalpy of the A-form being higher by 125 +/- 30 kJ X M-1; (3) the teritary structure of the 5S RNA does not unite secondary structure elements into a single cooperative unit even in the presence of 10 mM MgCl2; (4) the results of the analysis of the "equilibrium" part of heat capacity temperature functions and the A- and B-forms of the 5S RNA can be explained by melting of four cooperative blocks which interact with each other.