DNA replication and the nuclear envelope

Upon isolation of the nuclear membrane from cultured mouse leukemia L5178Y cells, approximately 1% of the total nuclear DNA was found to be attached to this structure. After pulse labeling of DNA and isolation of the nuclear membrane, the ratio of labeled DNA in the membrane fraction and in the rest of chromatin was compared. Results indicate that with a 3 min pulse, DNA in the membrane fraction showed slightly higher specific activity, but when the pulse was longer than 5 min there was no difference in the specific activities. Since the DNA fragment associated with the membrane fraction was found to be long enough to contain most of the DNA labeled during a 5 min pulse, the results obtained indicate that there is no preferential association of DNA to the nuclear envelope during initiation or elongation of DNA.