<i>IN VIVO</i> INDUCTION OF 4‐THIOURIDINE‐CYTIDINE ADDUCTS IN tRNA OF <i>E. COLI</i> B/r BY NEAR‐ULTRAVIOLET RADIATION*

Abstract

Abstract— Near‐ultraviolet (near‐UV; 320–405 nm) irradiation of Escherichia coli B/r induces the formation in vivo of 4 Srd‐Cyd adducts in transfer RNA, as evidenced by (1) fluorescence spectrum changes of tRNA extracted from irradiated cells and reduced with NaBH 4 , (2) thin‐layer chromatography on cellulose of hydrolysates of trichloroacetic acid‐precipitable extracts of irradiated cells, and (3) comparison of these findings with adduct formation induced by near‐UV irradiation of purified mixed tRNA from E. coli. The kinetics of induction of the 4 Srd‐Cyd adduct in vivo , and the near‐UV fluences required, provide strong support for our earlier hypothesis that formation of these adducts is responsible for near‐UV‐induced growth delay in E. coli.