Abstract
In the presence of optimal concentrations of Mg 2+, spermine and spermidine were found to stimulate rabbit globin mRNA-directed cDNA synthesis by Rauscher murine leukemia virus (R-MuLV) DNA polymerase. Stimulation of DNA synthesis did not occur with the polyamines putrescine or cadaverine, nor could exogenously provided salt or ammonium ions duplicate the stimulation. Analysis of the mechanism of stimulation showed that inclusion of spermine in reaction mixtures a) increased Vmax and decreased apparent Km with respect to the globin mRNA-oligo(dT) temṕlate-primer complex, and b) decreased the quantity of oligo (dT) required for optimal rates of cDNA synthesis on a fixed quantity of mRNA template. Genomic 70S RNA-directed cDNA synthesis was also stimulated by spermine addition to reaction mixtures, but only at supra-optimal RNA concentrations. Our results suggest that stimulation of R-MuLV DNA polymerase activity by polyamines is primarily due to stabilization of the enzyme-templateprimer initiation complex resulting in increased efficiency of initiation of cDNA synthesis.
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