INTRINSIC FLUORESCENCE OF S4 AND S7 E. COLI RIBOSOMAL PROTEINS*

Abstract

Abstract— Fluorescence properties of S4 and S7 ribosomal proteins, excited at 280 and 295 nm, have been studied; emission spectra, fluorescence quantum yields and lifetimes, effects of external quenchers (I‐ and Cs' ions) and of temperature. I t has been shown that the emissions are due to tyrosine and tryptophan for S4 and to tryptophan only for S7. The discussion of results showed that the emitfiny residues are not exposed in S4 and of two kinds, exposed (class a) or partially buried (class b), in S7. Above 35T, the single tryptophan of S4 is released into the aqueous medium, following thermal conformation changes of this protein. The spectral characteristics and the high values of quantum yields of S4 and S7 class b tryptophan emissions are consistent with the location of these residues in helical regions of the proteins. The absence of tyr‐ trp energy transfer in S4 may be due to a stretched conformation of this protein. The possibility of a further fluorescence study of the complexes between RNA and S4 and S7 proteins has been pointed out.