Abstract
Single stranded DNA (s.s.DNA) comprising 1-2% of the total nuclear DNA was isolated by an improved method of hydroxyapatite chromatography from native nuclear DNA3 of embryonic chick cells, labeled for several cell generations with 3H-thymidine. Small quantities of 3H-DNA were annealed with a large excess of unlabeled DNA or polysomal RNA from chick embryos. Hybridization kinetics (monitored by the use of SI nuclease digestion, hydroxyapatite chromatography and thermalfusion), indicated that s.s.DNA belongs to the non repetitious fraction of the cell genome. One third represents DNA sequences engaged in the transcription of messenger RNA's.