Effect of nucleotide polymorphism in cis-regulatory and coding regions on amylase activity and fitness in Drosophila melanogaster

In natural populations of Drosophila melanogaster, there are many amylase (AMY) isozymes encoded by the duplicated genes, but their adaptive significance remains unclear. One approach to elucidate this issue is to understand the molecular basis of functional differences between the allelic classes. In this study, the effects of nucleotide polymorphism in 5′-flanking (cis-regulatory) and coding regions on AMY activity were examined, both on glucose and starch food media and in larvae and adults, using three chimeric Amylase (Amy) genes, Amy^c111, Amy^c161 and Amy ^fc661. In this notation, the first number in the superscript indicates the sequence of the 5′-flnaking region (similar to Amy ¹ or Amy⁶), the second number refers to the coding region and the third number to the 3′-flanking region. We found that effect of nucleotide polymorphism in the coding region differed between larvae and adults. In larvae, the coding sequence of the Amy⁶ allele resulted in higher AMY activity than that of Amy¹ allele, indicating the post-transcriptional differences between them. The cis-regulatory region derived from the Amy⁶ allele resulted in higher AMY activity in both larvae and adults. Thus, two fitness components, developmental time and productivity, were measured to examine whether polymorphism in the cis-regulatory region between the two alleles has an effect on them, but no significant difference was detected. We raise the implications for the evolution of subfunctionalization in multigene families.