Molecular analysis of the yellow locus of Drosophila

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Abstract
The yellow (y) locus of Drosophila controls the pattern of pigmentation of the adult cuticle and larval mouth parts. Mutations of y belong to two phenotypic classes; type1 mutants exhibit a total loss of pigmentation from all parts of the cuticle and type 2 mutants show allele‐specific mosaic pigmentation patterns. We have cloned y by P‐element tagging followed by chromosome walking. We demonstrate that a 2.1‐kb transcript which spans 4.6 kb of genomic sequence is the y transcript. The location of this transcript and the putative protein it encodes has been defined by nuclease protection, primer extension and DNA sequencing experiments. A 12‐kb genomic fragment containing this transcript along with 2.8 kb of 5′‐flanking sequence and 4.6 kb of 3′‐flanking sequence is sufficient for the wild‐type expression of the larval and adult cuticle phenotypes in germ‐line transformants. The majority (12/14) of type1 mutants show structural lesions within exon coding portions of y. Most (6/7) of the type2 structural lesions map 5′ to the start of y transcription. One type2 mutant which contains an insertion within the 5′‐transcribed but non‐translated region appears to have resulted from the internal deletion of a P‐element associated with a type1 allele.