Pre-exposure to UV irradiation increases the transfer frequency of the IncJ conjugative transposon-like elements R391, R392, R705, R706, R997 and pMERPH and is recA+ dependent

The enteric conjugative transposon-like IncJ elements R391, R392, R705, R706 and pMERPH, all demonstrated increased conjugative transfer upon UV irradiation. The transfer frequency increased on average from its basal rate of 10−5 to 10−3 per recipient, upon pre-exposure to UV irradiation. However, the transfer frequency of R997, which was higher than the other IncJ elements at 10−3 per donor, showed a smaller increase. This effect was shown to be recA+ dependent in all cases. Using PCR primers directed outwards from the ends of the integrated R391 element it was observed that a circular intermediate of the element forms within the host, which has been proposed to be a transfer intermediate. Using real-time PCR, it was determined that the amount of the circular intermediate produced increased substantially upon UV irradiation.