Calcium-dependent priming of DNA synthesis in isolated rat liver nuclei

Nuclei isolated from rat liver in the absence of Ca²⁺ incorporate deoxyribonucleotides into added poly d(A-T) but not into their nuclear DNA, which is of high molecular weight. On exposure to Ca²⁺ the nuclear DNA is nicked and then serves as primer for incorporation of deoxyribonucleotides, in the presence of Mg²⁺, through the action of nuclear DNA polymerase. Incorporation of the chain-terminating arabinosyl analog araCMP ¹ 1 araCMP, araCTP: arabinofuranosyl analogs of CMP and CTP; EGTA: ethylene glycol-bis-(2-aminoethyl ether)-N,N′-tetraacetic acid. is a measure of Ca²⁺-dependent production of DNA primer sites in nuclei.