The Units of DNA Replication in Drosophila melanogaster Chromosomes
This extract was created in the absence of an abstract.
Excerpt
The DNA which must be replicated in a chromosome of Drosophila melanogaster appears to exist as a single molecule of double-stranded DNA, which, for the largest chromosomes, has a length of about 2.1 cm, or 62,000 kb1 (Kavenoff and Zimm, 1973). We have studied both the topography of the units of replication in this chromosomal DNA and the rate of replication per unit in two different classes of Drosophila nuclei which exhibit very different S phases. Our purpose is to define the factors which determine the overall replication rate for these giant DNA molecules.
The two classes are the rapidly replicating cleavage nuclei and the slowly replicating nuclei in cell cultures. At 24°C, the cleavage nuclei divide every 9.6 min in the syncytium of the egg for a period of about two hours after fertilization (Rabinowitz, 1941). Since interphase occupies 3.4 min of this doubling time, we presume that each...
