In vivo chain elongation of hepatic DNA: 1-beta-D-arabinofuranosyl cytosine sensitive steps.

The $\text{in vivo}$ chain elongation of rat liver DNA following partial hepatectomy was studied using alkaline sucrose gradients. DNA made in 5 min was less than 4 × 10⁷ daltons and that made in 30 min was heterodisperse and by 4 hr 75% of the DNA became larger than 1 × 10⁹ daltons. Administration of 1-β-D-arabinofuranosyl cytosine (ara-C) 5 min after thymidine-³H injection inhibited the chain elongation, whereas if given 30 minutes after thymidine-³H pulse did not inhibit the chain elongation. Thus the $\text{in vivo}$ chain elongation of rat liver DNA consists of at least two steps 1) a step sensitive to ara-C involving nucleotides addition and 2) the other insensitive to ara-C and probably involving ligation of polynucleotide chains.