Genomic clones coding for some of the initial genes expressed during Drosophila development.

Preblastoderm Drosophila embryos were made permeable and labeled in vivo with [32P]phosphate-containing medium. Cytoplasmic polyadenylylated RNA was extracted from these embryos and used to screen a library of Drosophila genomic DNA sequences cloned in phage lambda. Ten cloned sequences were selected for further study. These sequences were not complementary to mitochondrial DNA, nor did they contain the repeated nuclear genes coding for rRNA or histones. The cloned sequences each encode one or more unique genes expressed in preblastoderm embryos. RNA blot analysis indicated that some of these genes are also expressed at other times during embryogenesis. These results show that, in spite of the rapid nuclear divisions taking place during the preblastoderm stage, Drosophila nuclear genes are transcribed and that a subset of these genes show variable, stage-specific levels of expression during early embryogenesis.