Structural organization of the alpha-amylase gene locus in Drosophila melanogaster and Drosophila miranda.

Abstract

Chromosomal sites belonging to the alpha-amylase gene family have been identified in D. melanogaster and D. miranda and in the sibling species of miranda, pseudoobscura, and persimilis. Two sites occur in chromosome 2 of melanogaster; one contains the Amy gene locus (54A) and the other an amylase "pseudogene" (53CD). Two sites of homology exist at 73A and 78C and perhaps another at 81BC in chromosome 3 of pseudoobscura and persimilis and in the homologous regions of the X2 chromosome in miranda. The active Amy locus is apparently at 73A. The structural organization of cloned sequences from this multigene family in melanogaster and miranda is under analysis, with emphasis on the functional Amy gene region. Electrophoretic variants of amylase have served as invaluable tools in these studies. For melanogaster, their use as genetic markers enabled us to positively identify our lambda Dm65 clone of the Amy locus and to show that it contains two functional copies of the structural gene for alpha-amylase. Amylase isozymes are now being used in P element-mediated transformation experiments aimed at defining regulatory elements for the temporal and spatial control of amylase expression during development and in response to dietary glucose. In miranda, electrophoretic variants of amylase were useful in assigning the Amy locus to chromosome X2, and they continue to serve as essential markers in our study of the evolution of dosage compensation for amylase expression in males of this species. Restriction maps of the Amy locus in 7 strains of D. melanogaster indicate that despite the worldwide origins of the chromosome samples, all contain a duplication of the amylase structural gene at this locus regardless of whether they produce two alpha-amylase isozymes, a single variant, or none. We have aligned these maps with the genetic and cytological maps of chromosome 2R in melanogaster and assigned alleles for different amylase isozymes to either the proximal or distal Amy gene copy in a number of strains. Restriction site polymorphism is relatively limited at the Amy locus, but some strain-specific rearrangements exist. The locus of two strains with reduced amylase activity, Amy1 (CA 1) and Amy "null", contain anomalies--an insertion in the former and an inversion in the latter. Causal relationships are being sought between the level of amylase expression in these strains and the position of their respective anomalies.(ABSTRACT TRUNCATED AT 400 WORDS)