EFFECT ON N-7 AND C-8 SUBSTITUTION OF GUANINE IN DNA ON TM BUOYANT DENSITY AND RNA POLYMERASE PRIMING

The modification of calf thymus DNA by N-acetoxy-2-acetylaminofluorene substituting on the C-8 position of guanine and by β-propiolactone substituting on the N-7 position, is compared, using Tm, buoyant density and RNA polymerase priming activity as criteria. Both types of substitution lower Tm and buoyant density and abolish priming activity with RNA polymerase. C-8 substitution modifies buoyant density to a greater extent, and leads to a stable product. Tm and buoyant density of this adduct are not modified by incubation at 37°, while N-7 substituted DNA is hydrolyzed under this condition, leading to a lower Tm and broadened buoyant density band. Analogues of N-acetoxy-2-acetylaminofluorene such as N-acetoxy-1-acetylaminonaphthalene fail to modify DNA as measured by physical criteria. © 1969.