Nucleic Acids Research, 1983, Vol. 11, No. 16 5589-5602
© 1983
MOLECULAR BIOLOGY |
The binding of ribosomal protein SI to Sl-depleted 30S and 70S ribosomes. A fluorescence anisotropy study of the effects of Mg2+
Department of Chemistry, University of Nebraska Lincoln, NE 68588 Department of Biochemistry, University of Mississippi Medical Center Jackson, MS 39216, USA
Received February 28, 1983. Accepted July 13, 1983.
We have determined the equilibrium constants for the binding of AEDANS-labelled SI to Sl-depleted 30S and 70S ribosomes. For "tight" ribosomes,2+the association of SI increases with the sixth power of Mg concentration, but for 30S subunits and "loose" ribosomes, there is virtually no dependence of the association on Mg2+ over the same concentration range, 210 mM in Mg2+. The binding of SI to 70S ribosomes at 10 mM Mg2+ is stabilized by 2 kcal/mol compared to the binding to 30S subunits. When intact SI binds to tight ribosomes, the fluorescence anisotropy is that for virtually complete rotational immobilization. The anisotropies vary considerably with the preparation and treatment of both SI and ribosomes and these variations are detailed here. The results suggest the linkage of Mg2+ -dependent conformational changes in the intact ribosomes, perhaps including rRNA, and the binding of SI.