Demonstration of ribosome-dependent photoinduced chain breakage of the 16S ribosomal ribonucleic acid component of the Escherichia coli 30S ribosomal subunit.

The effects of 253.7-nm radiation on the structural integrities of free and ribosome-bound 16S ribosomal ribonucleic acid (rRNA) have been elucidated. Exposure of aqueous solutions of Escherichia coli 30S ribosomal subunits to 253.7-nm radiation results in RNA-chain scission and the formation of single-stranded breaks in double-stranded regions of the ribosome-bound 16S rRNA. The minimum doses of incident 253.7-nm radiation required for the first detection of the two types of RNA chain breaks are 2 X 10(20) quanta for single-strand breaks in double-stranded regions of the ribosome-bound 16S rRNA,and at least 5 X 10(20) quanta for RNA-chain scission. In contrast to the photosensitivity of ribosome-bound 16S rRNA toward chain breakage, free 16S rRNA seems to be resistant toward photoinduced chain breakage at doses of incident 253.7-nm radiation up to at least 10(21) quanta.