Incorporation of deoxythymidine triphosphate into nuclear DNA of developing frog embryos in vitro

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The rate of incorporation of labeled precursor into DNA of isolated nuclei decreased from gastrulation to the tailbud stage in developing frog embryos. The addition of saturating amounts of calf thymus DNA revealed that the activities of the enzyme(s) which incorporates deoxythymidine triphosphate (dTTP) into DNA in vitro decreased over this period. Native DNA was a better template than denatured DNA. The addition of a purified microbial DNA polymerase to gastrula and tailbud nuclei showed that the chromatin DNA of the later stage is a poorer template for the enzyme. The activity of the enzyme(s) which accounts for dTTP incorporation into DNA in vitro was higher during the early S period of neurulae than for late S and higher for late S than early S of tailbuds when nuclei were isolated from partially synchronized cells. For both the randomly dividing and partially synchronized cells, the activity of the enzyme(s) incorporating dTTP into DNA in vitro is correlated with the level of incorporation of labeled precursor into DNA in vivo.