Evidence for photoinduced cross-linkage, in situ, of 30S ribosomal proteins to 16S rRNA.

The effects of ultraviolet radiation on the 30S ribosomal subunit of Escherichia coli were studied. Irradiation in aqueous solution under anaerobic conditions resulted in a dose-dependent decrease in the separability of the rRNA and protein components of the 30S ribosomal subunit in 4 M urea-3 M LiC1. The results of gel filtration studies of the irradiated ribosomes before and after treatment with pancreatic ribonuclease indicated that the decrease in separability of the ribosome components was a result of the photoinduced formation of covalent RNA-protein cross-links. The number of covalent cross-links was estimated to correspond to less than 3 per 10,000 daltons of ribosomal proteins. One-dimensional gel electrophoresis studies of the course of the photoinduced cross-linkage reaction indicated that cross-linkage of individual 30S ribosomal proteins to the 16S rRNA proceeds in two dose-dependent steps. The first step requires an input of 1 X 10(20) quanta of 253.7 -nm radiation and results in the cross-linkage of at least five ribosomal proteins to the 16S rRNA. The second step requires a total input of 2 X 10(20) quanta of 253.7 -nm radiation, and results in the cross-linkage of most of the remaining 30S ribosomal proteins to the 16S rRNA.