Replicating DNA molecules from eggs of Drosophila melanogaster.

Abstract

Eggs ofDrosophila melanogaster were lysed with sodium dodecyl sulphate within 110 minutes after laying and the lysate prepared for electron microscopy by the protein monolayer technique. Long, non-circular DNA molecules were found with a form suggesting they contained either a single replicated region, or two, three or four replicated regions arranged in tandem. Each replicated region was delimited by two forks. The two segments of DNA spanning the region between the forks were approximately equal in length and appeared to be totally or almost totally double-stranded. The appearance of replicating molecules was not altered by digestion with pronase or treatment with phenol or chloroform. The lengths of replicated regions varied from 0.2 μ to 22.1 μ with a mean value of 2.97 μ. The distances between midpoints of adjacent tandemly arranged replicated regions ranged from 1.2 μ to 9.7 μ with a mean value of 3.87 μ. Circular molecules found in these preparations, and presumed to be of mitochondrial origin, were estimated from comparative length measurements with circular double-stranded DNA molecules from the bacteriophages lambda, φX174 and fd to have a molecular weight of 12.36 X 106 daltons.