Molecular analysis of the swallow gene of Drosophila melanogaster.

We report the cloning and molecular characterization of the swallow gene, a maternal-effect gene of Drosophila melanogaster. Maternal-effect genes are transcribed only during oogenesis; one such gene, bicoid, encodes a message that is localized at the anterior end of oocytes, eggs, and early embryos. swallow+ activity is necessary during oogenesis for bicoid message localization. We show here that a fragment of a previously identified clone, introduced into the genome by P-element-mediated transformation, is able to rescue the maternal-effect lethality of swallow mutants, confirming the identity of this clone as swallow. By in situ hybridization, we show that swallow message is synthesized in nurse cells during oogenesis but is not localized along either the anterior-posterior or dorsal-ventral axes. We have confirmed an earlier finding that the localization of bicoid message is defective in swallow- oocytes and eggs.