GENETIC-ANALYSIS OF THE BRAHMA GENE OF DROSOPHILA-MELANOGASTER AND POLYTENE CHROMOSOME SUBDIVISIONS 72AB

The brahma gene is required for activation of the homeotic genes of th e Antennapedia and bithorax complexes in Drosophila, We have isolated and characterized 21 mutations in brahma. We show that both maternal a nd zygotic functions of brahma are required during embryogenesis. In a ddition, the severe abnormalities caused by loss of maternal brahma ex pression show that the homeotic genes are not the only targets for bra hma activation. The complex pattern of interallelic complementation fo r the 21 brahma alleles suggests that brahma may act as a multimer. In addition to mutations in brahma, we have isolated mutations in four o ther essential genes within polytene chromosome subdivisions 72AB. Bas ed on a compilation of similar studies that include about 24% of the g enome, we estimate that about 3600 genes in Drosophila can mutate to c ause recessive lethality, with fewer than 900 additional genes essenti al only for gametogenesis. We have identified three times more transcr ipts than lethal complementation groups in 72AB. One transcript in 72A B is the product of the essential arflike gene and encodes a member of the ARF subfamily of small GTP-binding proteins. Two other transcript s are probably the products of a single gene whose protein products ar e similar to the catalytic subunits of cAMP-dependent protein kinases.