Structure of transcripts from the homeotic Antennapedia gene of Drosophila melanogaster: two promoters control the major protein-coding region.

Abstract

The Antennapedia (Antp) homeotic gene of Drosophila melanogaster regulates segmental identity in the thorax. Loss of Antp function results in altered development of the embryonic thoracic segments or can cause legs to be transformed into antennae. Certain combinations of Antp recessive lethal alleles complement to permit normal development. The structure of the Antp gene, analyzed by sequencing cDNA clones and exons and by transcript mapping, revealed some of the basis for its genetic complexity. It has two promoters governing two nested transcription units, one unit 36 and one 103 kilobase pairs (kb) long. Both units incorporated the same protein-coding exons, all of which are located in the 3'-most 13 kb of the gene. The two promoters resulted in the attachment of either of two long noncoding leader sequences (1.5 and 1.7 kb) to a 1.1-kb open reading frame. Both transcription units used the same pair of alternative polyadenylation sites 1.4 kb apart; the choice of sites was developmentally regulated. Some of the mutations that disrupt the larger transcription unit complemented a mutation affecting the smaller one. Dominant mutations that transform antennae into legs split the gene but left the coding exons intact. The encoded protein has unusually long runs of glutamine and a homeodomain near the C terminus.

Function and misfunction of the two promoters of the Drosophila Antennapedia gene.

“…Transcripts begin at alternative exons, which leads to different 5' sequences preceding the open reading flame; and transcripts end at alternative polyadenylation sites, which leads to two types of 3' untranslated sequences. Because the transcription initiation sites at exon 1 and exon 3 are separated by 70 kb, it has been proposed that these RNAs originate from different promoters (Laughon et al 1986;Schneuwly et al 1986;Stroeher et al 1986). In this paper we present functional proof that the two start sites represent independent promoters.…”

“…The Antp gene is unusually large; its eight exons span over 100 kilobase pairs (kb)of genomic DNA Scott et al 1983;Laughon et al 1986;Schneuwly et al 1986). The open reading flame is contamed in four major transcript types, which are generated by alternative choices at two steps in RNA synthesis: initiation and 3' processing {Fig.…”

“…Previous investigations of the Antp gene did not reveal any of the above functional distinctions between the initiation sites. First, the altemative 5' exons do not contain any portion of the open reading flame; therefore, they cannot encode proteins with different 5' domains (Laughon et al 1986;Schneuwly et al 1986;Stroeher et al 1986). Although alternative splicing does produce short sequence differences within the open reading frame, no association with a particular promoter has been observed (V. Stroeher, C. Gaiser, and R. Garber, in prep.).…”

A family of dynein genes in Drosophila melanogaster.

“…Total RNA was prepared from 0-12-h embryos, adult females, and adult males by guanidinium isothiocyanate extraction and LiCl precipitation (Laughon et al, 1986). The RNA was reverse transcribed and subsequently amplified by the PCR (Kawasaki et al, 1988).…”

A neuron-specific enhancer of the Drosophila dopa decarboxylase gene.

“…A number of these genes require large regulatory regions to generate a complex pattern of developmental expression (Bender et al 1983;Laughon et al 1986;Peifer and Bender 1986). It is clear, however, that the generation of a cell-specific pattern of gene expression does not necessarily require such massive expanses of regulatory DNA.…”