Enzymic incorporation of deoxyribonucleotides into deoxyribonucleic acid by mammalian testis

Testicular enzymes which catalyze the incorporation into DNA of deoxyribonucleotides derived from deoxyribonucleoside triphosphates are most abundant in the supernatant fluid obtained after ultracentrifugation of rat testis homogenates. Studies on the incorporation of deoxyribonucleotides by fractions obtained from such crude soluble extracts by precipitation with ammonium sulfate suggest that the principal type of enzyme involved is a “replicative” DNA nucleotidyl transferase (DNA polymerase). The enzymic reactions exhibit a requirement for all four deoxyribonucleoside triphosphates, Mg ++, and DNA (preferably heat-denatured). Attention is given to effects of glycerol on the stability of the enzymic activity and on the priming of the reactions by native and heat-denatured DNA's. Other factors influencing the deoxyribonucleotide incorporations are discussed. The DNA polymerase activity of the newborn rat testis is very high, and declines markedly at puberty. In adult rats, DNA polymerase levels are lowered in unilaterally cryptorchid testes.