title: 4-Thiouridine triggers both growth delay induced by near-ultraviolet light and photoprotection.
abstract: 4-Thiouridine, a rare nucleoside present in Escherichia coli tRNAs, has been recently proposed to be the major chromophore leading to near-ultraviolet (315-400-nm)-induced growth delay. Here this is established by the isolation of mutants exhibiting a reduced growth delay. The selection procedure involves several successive cycles of 365-nm illumination of the cells in the stationary phase, followed by growth for two or three generations. After the eighth cycle, the level of 4-thiouridine in the culture decreases to 20% of the original level and all individual clones tested show a 4-thiouridine deficiency. One mutant exhibiting a complete lack of 4-thiouridine in its tRNAs has been characterized. In the dark the growth characteristics of the mutant and of the parental strain are indistinguishable. In contrast after near-ultraviolet illumination the nuv mutation abolishes the growth delay and considerably reduces the photoprotection efficiency.
mesh_terms: D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D009154:Mutation; D010782:Photolysis; D012343:RNA, Transfer / Q000032:analysis; D013873:Thionucleotides / Q000032:analysis; D013891:Thiouridine / Q000378:metabolism*; D014466:Ultraviolet Rays; D014529:Uridine / Q000032:analysis
chemical_list: D013873:Thionucleotides; D013891:Thiouridine; D012343:RNA, Transfer; D014529:Uridine