exonucleases specific for either 3 ' ends ( escherichia coli exonuclease iii ) or 5 ' ends ( bacteriophage t7 gene 6 exonuclease ) of nascent dna chains have been used to determine the number of nucleotides from the actual sites of dna synthesis to the first nucleosome on each arm of replication forks in simian virus 40 ( sv40 ) chromosomes labeled with [ 3h ] thymidine in whole cells .
C0012854
dna
C0598312
dna