Influence of ribosides on ultraviolet resistance of Escherichia coli: role of deoxyribonucleic acid synthesis in the ultraviolet resistance enhancement after amino acid prestarvation.

Changes in the resistance of cells of Escherichia coli B/r Hcr(+)thy(-)trp(-) to ultraviolet radiation were investigated after the following pretreatments: (i) amino acid starvation which, according to previous conclusions, enabled the cells to complete replication cycles of deoxyribonucleic acid (DNA); (ii) amino acid starvation during which the synthesis of DNA was arrested by the addition of 50 mug of cytidine per ml. The results showed that the enhancement of resistance observed after amino acid prestarvation was in correlation with the amount of DNA which was synthesized during the amino acidless period. The enhancement of resistance can be abolished by the addition of the riboside at any phase of the starvation period. This shows that the enhancement of resistance was not a consequence of the total inhibition of metabolism but of unbalanced growth which evoked the completion of replication cycles of DNA.