Structure and transcription of the Drosophila melanogaster vermilion gene and several mutant alleles.

The nucleotide sequence and intron-exon structure of the Drosophila melanogaster vermilion (v) gene have been determined. In addition, the sites of several mutations and the effects of these mutations on transcription have been examined. The major v mRNA is generated upon splicing six exons of lengths (5' to 3') 83, 161, 134, 607, 94, and 227 nucleotides (nt). A minor species of v mRNA is initiated at an upstream site and has a 5' exon of at least 152 nt which overlaps the region included in the 83-nt exon of the major v RNA. The three v mutations, v1, v2, and vk, which can be suppressed by mutations at suppressor of sable, su(s), are insertions of transposon 412 at the same position in exon 1, 36 nt downstream of the major transcription initiation site. Despite the 7.5-kilobase insertion in these v alleles, a reduced level of wild-type-sized mRNA accumulates in suppressed mutant strains. The structure and transcription of several unsuppressible v alleles have also been examined. The v36f mutation is a B104/roo insertion in intron 4 near the splice donor site. A mutant carrying this alteration accumulates a very low level of mRNA that is apparently polyadenylated at a site within the B104/roo transposon. The v48a mutation, which deletes approximately 200 nt of DNA, fuses portions of exons 3 and 4 without disruption of the translational reading frame. A smaller transcript accumulates at a wild-type level, and thus an altered, nonfunctional polypeptide is likely to be synthesized in strains carrying this mutation. The v(H2a) mutants has a P element insertion in exon 6 within the coding region.