A new homeotic mutation in the Drosophila bithorax complex removes a boundary separating two domains of regulation.
The bithorax complex specifies the identity of parasegments 5-14 of Drosophila. Although nine parasegment-specific functions, abx/bx, bxd/pbx and iab-2 to iab-8,9 have been identified, the whole bithorax complex appears to encode only three classes of proteins, Ubx, abd-A and Abd-B. Many observations suggest that the parasegment-specific functions act as positive cis-regulatory elements of Ubx, abd-A and Abd-B. We report the molecular genetics of a new gain-of-function mutation, Fab-7, which transforms parasegment 11 into parasegment 12. Induction of Abd-B mutations in cis (one of which removes the Abd-B homeobox) causes reversion of the dominant phenotype, demonstrating that Fab-7 misregulates Abd-B. A 4 kb deletion, 30 kb downstream from the Abd-B transcription unit, is solely responsible for the Fab-7 phenotype. We consider that the parasegment-specific functions lie in DNA domains that are sequentially and independently 'opened' along the chromosome. Once a domain is opened, the cis-regulatory sequences within it can carry out their function. We propose that the Fab-7 deletion removes a boundary separating the iab-6 and iab-7 cis-regulatory regions (the functions specific for parasegments 11 and 12) allowing the open configuration of iab-6 to invade iab-7 in parasegment 11. This is strongly supported by our finding that Fab-7 can be caused to revert by lesions not only in iab-7 but also in iab-6.
Gyurkovics
H
H
Biological Research Center, Hungarian Academy of Sciences, Szeged.
Gausz
J
J
Kummer
J
J
Karch
F
F
D000818:Animals; D015139:Blotting, Southern; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D004247:DNA / Q000032:analysis / Q000235:genetics; D004330:Drosophila / Q000033:anatomy & histology / Q000235:genetics* / Q000528:radiation effects; D005260:Female; D005786:Gene Expression Regulation; D005801:Genes, Homeobox; D005838:Genotype; D007814:Larva; D008297:Male; D009154:Mutation
D004247:DNA