Localization of L11 on the Escherichia coli ribosome by singlet-singlet energy transfer

Isolated Escherichia coli ribosomal protein L11 was labeled with maleimidyl derivatives of coumarin or fluorescein at the thiol group of its single cysteine, then reconstituted singly or in pairs with other fluorescently labeled ribosomal components. The characteristics of fluorescence from the labeled protein were studied and its distance to other components was determined by non-radiative energy transfer. The distance between probes on L11 and cysteine residues on other proteins or the 3' end of the ribosomal RNAs were found to be: S1, 7.4-8.3 nm; S21, 7.6 nm; 23S RNA, 6.9 nm; 5S RNA, 7.6 nm; 16S RNA, greater than 8.5 nm. Considered together with previously published results these distances indicate that the location of L11 in the 50S subunit is below the lateral protuberance characterized by L7/L12.