Transcription of the white locus in Drosophila melanogaster

Abstract

The white locus has a distal region where structural mutations occur and a proximal region where regulatory mutations occur. To better understand the molecular basis of this genetic organization, white locus transcription was analyzed. A 2.7-kilobase transcript comprising 0.0005% of poly(A)-RNA was detected in RNA prepared from pupae or adults. The structure of this transcript helps clarify some unusual genetic properties of the locus. There is a small 5'' exon separated from the majority of the sequences found in the mature RNA by an intron of .apprxeq. 2.8 kilobases. This 5'' exon is from the proximal region of the locus, whereas the main body of the RNA maps to the distal region. The mutationally silent region between the proximal and distal regions corresponds to the large intron. The family was identified and the exact location of a number of transposable element insertions within the locus was determined. Transposable element insertions within introns can be without phenotypic effect. The effect on the white transcript of the zeste mutation, which represses white locus expression as judged by eye color phenotype, was investigated. The RNA was unchanged in size or abundance in poly(A)-RNA from adult flies. The zeste-white interaction does not occur by simply repressing transcription of the white locus in all tissues.