The RNA polymerases of Drosophila melanogaster during early development.

The enzymatic basis for the changing rates of RNA synthesis in early Drosophila development has been examined through a description of the multiple forms, relative proportions, and total and specific activities of the RNA polymerases of the Drosophila embryo. Six chromatographically identifiable forms of RNA polymerase are detectable in embryos (Forms Ia, Ib, IIa, IIb, IIIa, IIIb), one of which (Form IIa) appears to be cytoplasmically localized and is present only in unfertilized eggs and pregastrular embryos, while another (Form IIb) appears only at gastrulation and remains throughout the remainder of development. The total and specific activities of the embryonic RNA polymerases are related to the patterns of embryonic RNA synthesis and to the nuclear and cellular events of holometabolous development.