DISTRIBUTION AND EVOLUTION OF INTRONS IN DROSOPHILA AMYLASE GENES

While the two amylase genes of Drosophila melanogaster are intronless, the three genes of D. pseudoobscura harbor a short intron. This raise s the question of the common structure of the Amy gene in Drosophila s pecies. We have investigated the presence or absence of an intron in t he amylase genes of 150 species of Drosophilids. Using polymerase chai n reaction (PCR), we have amplified a region that surrounds the intron site reported in D. pseudoobscura and a few other species. The result s revealed that most species contain an intron, with a variable size r anging from 50 to 750 bp, although the very majoritary size was around 60-80 bp. Several species belonging to different lineages were found to lack an intron. This loss of intervening sequence was likely due to evolutionarily independent and rather frequent events. Some other spe cies had both types of genes: In the obscura group, and to a lesser ex tent in the ananassae subgroup, intronless copies had much diverged fr om intron-containing genes. Base composition of short introns was foun d to be variable and correlated with that of the surrounding exons, wh ereas long introns were all A-T rich. We have extended our study to no n-Drosophilid insects. In species from other orders of Holometaboles, Lepidoptera and Hymenoptera, an intron was found at an identical posit ion in the Amy gene, suggesting that the intron was ancestral.