Molecular organization of an individual Drosophila polytene chromomere: transcribed sequences in the 10A1-2 band.

Complete cloning of the DNA in the cytogenetic region 9F12-10A7 has allowed us to analyze the fine structure of an individual polytene chromomere in Drosophila melanogaster. In this report we identify the transcriptionally active fragments within the 10A1-2 band. At least 22 DNA fragments representing multiple distinct transcription units are active during embryogenesis, in third-instar larva or in isolated larval tissues. The transcribed fragments are significantly (at least sevenfold) more numerous than the three genetically defined complementation groups in the 10A1-2 band. One of the transcriptionally active zones detected encompasses a previously unsuspected homologue of the genes Delta and Serrate.