The morphogenetic and regulatory functions of the Drosophila Abdominal-B gene are encoded in overlapping RNAs transcribed from separate promoters.
The Abdominal-B (Abd-B) gene of the Drosophila bithorax complex is a homeotic gene with two subfunctions: the morphogenetic element required for specifying the identity of parasegments (PS) 10-13 and the regulatory element that represses the expression of other homeotic genes in PS14. Here, we provide evidence that four classes of overlapping transcripts are generated from the Abd-B gene and characterize three of the transcripts in detail. We determined the transcription initiation sites for the 4.6- and 3.4-kb RNAs and show that they are generated from separate promoters. Both of these transcripts are present throughout the period during which the Abd-B subfunctions are required. A mutation that inactivates the morphogenetic function is associated with a 411-bp deletion of the initiation site for the 4.6-kb RNA. The regulatory function mutations disrupt the transcription unit for the 3.4-, but not the 4.6-kb, RNA. These results support the assignment of the morphogenetic function to the 4.6-kb RNA and the regulatory function to the 3.4-kb RNA. A 7.8-kb RNA expressed during embryogenesis may also contribute to the regulatory function. Sequence analysis of cDNAs indicates that the 4.6-kb RNA encodes a 55-kD protein (the m protein), whereas the 3.4-kb RNA encodes a 30-kD protein (the r protein). The m and r proteins share a carboxy-terminal sequence that includes the homeo domain, but the r protein lacks a glutamine-rich amino-terminal domain found in the m protein.
Zavortink
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Howard Hughes Medical Institute, Department of Human Genetics, University of Utah School of Medicine, Salt Lake City 84132.
Sakonju
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D000005:Abdomen; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004330:Drosophila / Q000235:genetics*; D005091:Exons; D005801:Genes, Homeobox; D005809:Genes, Regulator; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D012313:RNA / Q000235:genetics; D015183:Restriction Mapping; D014158:Transcription, Genetic
D012313:RNA; D004247:DNA