Effects of transposable elements on the expression of the forked gene of Drosophila melanogaster.

The products of the forked gene are involved in the formation and/or maintenance of a temporary fibrillar structure within the developing bristle rudiment of Drosophila melanogaster. Mutations in the forked locus alter this structure and result in aberrant development of macrochaetae, microchaetae and trichomes. The locus has been characterized at the molecular level by walking, mutant characterization and transcript analysis. Expression of the six forked transcripts is temporally restricted to mid-late pupal development. At this time, RNAs of 6.4, 5.6, 5.4, 2.5, 1.9 and 1.1 kilobases (kb) are detected by Northern analysis. The coding region of these RNAs has been found to be within a 21-kb stretch of genomic DNA. The amino terminus of the proteins encoded by the 5.4- and 5.6-kb forked transcripts contain tandem copies of ankyrin-like repeats that may play an important role in the function of forked-encoded products. The profile of forked RNA expression is altered in seven spontaneous mutations characterized during this study. Three forked mutations induced by the insertion of the gypsy retrotransposon contain a copy of this element inserted into an intron of the gene. In these mutants, the 5.6-, 5.4- and 2.5-kb forked mRNAs are truncated via recognition of the polyadenylation site in the 5' long terminal repeat of the gypsy retrotransposon. These results help explain the role of the forked gene in fly development and further our understanding of the role of transposable elements in mutagenesis.