James G. Wetmur

Renaturation of bacteriophage φX174 DNA-RNA hybrid: RNA length effect and nucleation rate constant

Abstract A one to one RNA-DNA hybrid was synthesized using bacteriophage φX174 DNA as a template for the Escherichia coli RNA polymerase system. The renaturation rate for the hybrid was found to vary as the square root of the molecular weight of the RNA. The RNA molecular weights were determined using a standardized dimethylsulfoxide, cesium sulfate equilibrium density gradient. The optimum nucleation rate constant for the renaturation of the hybrid in 0.4 m -sodium chloride was found to be 1.3 × 105, as compared with to 1.7 × 105 for DNA renaturation.

Length dependence of the kinetic complexity of mouse satellite DNA

Abstract Treatment of renatured mouse satellite DNA with the single stranded DNA specific endonuclease Sl leads to the isolation, with no losses, of regions of length, L ≤ 56±28, from molecules containing several such regions. The rate of renaturation is observed to be an unusual function of length, extrapolating to an apparent complexity, N ≤ 36±9. The results are consistent with a model of tandem, spaced, repetitions where multiple nucleations may occur between two strands containing the complementary repetition units.

Physical studies of chloroacetaldehyde labelled fluorescent DNA

Abstract The reaction of chloroacetaldehyde with denatured DNA produces a fluorescent DNA where both the adenine and cytosine bases are modified. The rate of modification of DNA by chloroacetaldehyde was measured using the absorption spectrum shift. The depolarization and quantum yield of native DNA and denatured DNA were investigated as a function of temperature. The melting points and the renaturation rates of a series of derivative DNAs were investigated. The melting point was decreased by 1.3°C for each base modified per 100 base pairs corresponding to a 2.8 Kcal destabilizing free energy per mismatched base pair. The renaturation rate of the derivative DNA is reduced by a factor 2 when the melting temperature is lowered by 13°C.