RIBOSOME DEGRADATION IN ULTRAVIOLET LIGHT-DAMAGED BACTERIA STARVED FOR AN AMINO ACID

Degradation of RNA and of 30-S and 50-S ribosomes occurred when Escherichia coli H/r 30R cells were exposed to 400 ergs/mm2 of ultraviolet light and then incubated without arginine, a required amino acid. Under these conditions, the ribosomes remained stable for 1 h, but rapid breakdown began thereafter and eliminated the greater part of the ribosomes by 2 h. Arginine prevented most of the breakdown. Both the photoreversible pyrimidine dimer and non-photoreversible damage appeared to result in breakdown, but at this ultraviolet light dose most of the damage was not photoreversible. If 30 min of postirradiation incubation with arginine was allowed prior to incubation without the amino acid, little degradation occurred on subsequent arginineless incubation, indicating that dark repair processes dependent on protein synthesis are capable of removing the cause of the breakdown, presumably through repair of damage to DNA resulting in recovery of capacity for DNA replication. © 1969.