[DNA synthesis in isolated nuclei of Misgurnus fossilis loach embryos. II. Sedimentation of newly-formed DNA in an alkaline sucrose concentration gradient. Effect of calcium ions].

Three fractions of nascent DNA labeled with [3H]dCTP in isolated nuclei of Misgurnus fossilis embryos were observed after sedimentation in alkaline sucrose: 1) high-molecular-weight DNA strands larger than 3000 nucleotides; 2) fragments of DNA with average length about 200 nucleotides; 3) low-molecular-weight DNA fragments shorter than 100 nucleotides. The labeled DNA was accumulated in the high-molecular-weight fraction (1) with an increase of incubation time. This process indicated the sealing of Okazaki fragments to parental DNA in the course of DNA replication. Adenosine diphosphate stimulated the label accumulation in larger DNA fragments. Embryo nuclei contain Ca-dependent desoxyribonuclease which can digest both exogenous and endogenous DNA DNase I treatment of nuclei dramatically stimulated the label incorporation into nuclear DNA.