Steroid induced single strand breaks in DNA mediated by active oxygen species and its biological consequences

A mutagenic steroidal derivative (3 beta-Acetoxy-5 alpha-Cholestano[6 alpha,5-d']1'-3'oxathiolane-2' thione) structurally related to cholesterol caused strand scission and induced nicks in calf thymus, supercoiled pBR322 and single stranded M13 mp8 phage DNAs. S1 nuclease hydrolysis, reaction with pBR322 and M13 phage DNA as well as treatment of E. coil mutant strains and phage was used to evaluate the effect of test steroid on the DNA molecule. The strand scission/nicking of DNA by the test steroid was enhanced by some metal ions, especially the Cu(II). Scavengers of active oxygen radical species significantly inhibited the S1 nuclease hydrolysis by the test steroid indicating the major role of active oxygen species in DNA strand scission and nicking. The steroid brought about the DNA degradation even in the absence of S1 nuclease. There was an appreciable reduction in the survival of steroid treated polA and lig mutants of E. coli K12 compared to the wild type strain. Phage on steroid treatment also lost its plaque forming units (P.F.U.) which was more pronounced in the polA and rec A background.