Regulation of glucose-6-phosphate dehydrogenase activity by a presumptive extrachromosomal factor in Drosophila melanogaster.

Abstract

We have previously reported that the major regulatory factor responsible for an increase of glucose-6-phosphate dehydrogenase in Drosophila melanogaster may not be linked to any of chromosome 1, 2 and 3 (Tanda and Hori 1982, 1983). Recently, an X-linked mutation that gives rise to flies of very high enzyme activity was found in some progenies of a strain which formerly had the factor unlinked to the X chromosome. This mutation appears to be due to insertion of the regulatory factor into the X chromosome.Several strains which were so constructed as to be homozygous for the X chromosomes of male mutants exhibited high enzyme activities at generation 0 without exception, but decreases in enzyme activity occurred in the succeeding generations. Reasoning that such decreases might be due to excision of the regulatory factor or its translocation to somewhere else in the genome where it becomes silent, X chromosomes were extracted from males showing high and low enzyme activities, and their isogenic progenies were assayed for enzyme activity. The results showed that low-activity males produced low-activity progenies, whereas high-activity males produced high-activity progenies, thus suggesting that the sampled males were hemizygous for an X chromosome with or without the functional regulatory factor.In view of these and other findings, the possibility may be envisaged that there may be an extrachromosomal factor in the nuclei of D. melanogaster which is capable of stimulating the G6PD activity, and could occasionally be inserted into the X chromosome.