The Effect of U.V.-irradiation on λ DNA Transcription

Summary

The effect of U.V.-irradiation of template DNA has been studied in vitro in the E. coli RNA polymerase system with native and U.V.-treated λ DNA. λ DNA is more susceptible to U.V. than is calf-thymus DNA, yet a residual activity is observed at a U.V. dose of 0·5 + 10⁴ erg/mm². From the kinetic analysis of the reaction and the incorporation of γ ³²P-labelled nucleoside triphosphates, it seems reasonable to conclude that U.V.-irradiation probably does not affect the DNA initiation sites, recognizable by RNA polymerase. The transcription products made with U.V.-irradiated λ DNA are assymmetrical, and hybridized to the right half (R) and the left half (L) of λ DNA with the ratio of R/L = 4/1, and they show a lower hybridizability than the transcripts with native λ DNA. The initiation sites recognizable by RNA polymerase seem to be the same on both native and U.V.-irradiated λ DNA, though the transcription of U.V.-treated λ DNA appears to terminate with rather short RNA chains.