The pattern of DNA polymerase activity in developing Drosophila melanogaster has been studied in seven stages of embryonic development as well as in unfertilized eggs. The crude polymerase-containing extracts, most likely of cytoplasmic origin, utilize, in the following order of decreasing template efficiency, "activated" calfthymus DNA, poly(A)-oligo(dT), and poly(A) oligo(U). The highest enzyme levels occur in unfertilized eggs; the activity remains high during the first 9 hr of embryogenesis, but shows a progressive decline in the later stages. Deoxyribonuclease exhibits a similar trend. The unfertilized eggs of two genotypically different females had nearly identical levels of DNA polymerase.The enzymic mechanisms of nucleic acid formation, and especially their alterations, during cellular differentiation offer an interesting field of study, as has been emphasized in previous papers from this laboratory (1, 2). The present report extends our studies, originally done with the developing chicken embryo, to another eukaryotic organism whose developmental stages are defined precisely and which has the additional advantage of being suitable for genetic analysis. We present here a survey of DNA polymerase activity during the development of Drosophila melanogaster, beginning with the unfertilized egg and extending through the several stages of embryonic growth. (2) Poly(A) -poly(U) (1.4:1, w/w), prepared similarly, using poly(U), s2o = 7.1, supplied by P.' L. Biochemicals. (3) Poly(A) * oligo(dT) (1.2: 1, w/w); the same poly(A) preparation was hybridized with oligo(dT). The latter was obtained by treatment of 400 ,ug of poly(dT) with sheepkidney nuclease (7) for 30 min (2 units/ml of incubation mixture), followed by inactivation of the enzyme (700, 4 min). (4) Poly-(A) -oligo(U) (1.4:1, w/w); the same poly(A) specimen was hybridized with oligo(U), produced by treatment with the nuclease for 15 min (800 ,ug of polymer, 2 units of * The duration of this procedure, 0.5 hr, is included in the specified age of the eggs. Thus, since for the earliest embryonic age the eggs were frozen directly after the collection period of 1.5 hr, the age of these embryos ranged from 0.5-2 hr. 2946
MATERIALS AND METHODS
Drosophila melanogaster