ABSTRACT
The evolutionary significance of molecular variation is still contentious, with much current interest focusing on the relative contribution of structural changes in proteins versus regulatory variation in gene expression. We present a population genetic and biochemical study of molecular variation at the malic enzyme locus (Men) in Drosophila melanogaster. Two amino acid polymorphisms appear to affect substrate-binding kinetics, while only one appears to affect thermal stability. Interestingly, we find that enzyme activity differences previously assigned to one of the polymorphisms may, instead, be a function of linked regulatory differences. These results suggest that both regulatory and structural changes contribute to differences in protein function. Our examination of the Men coding sequences reveals no evidence for selection acting on the polymorphisms, but earlier work on this enzyme indicates that the biochemical variation observed has physiological repercussions and therefore could potentially be under natural selection.
Subject(s)
Drosophila melanogaster/enzymology , Insect Proteins/chemistry , Malate Dehydrogenase/chemistry , Polymorphism, Genetic , Regulatory Sequences, Nucleic Acid , Amino Acid Sequence , Animals , Chromosomes, Insect/genetics , Drosophila melanogaster/genetics , Enzyme Activation , Enzyme Stability , Evolution, Molecular , Female , Gene Expression Regulation, Enzymologic , Genes, Insect , Genetic Loci , Genetic Variation , Genetics, Population , Genotype , Insect Proteins/genetics , Malate Dehydrogenase/genetics , Male , Sequence Analysis, DNA , Solubility , Substrate SpecificityABSTRACT
Regulation of transcription can be a complex process in which many cis- and trans-interactions determine the final pattern of expression. Among these interactions are trans-interactions mediated by the pairing of homologous chromosomes. These trans-effects are wide ranging, affecting gene regulation in many species and creating complex possibilities in gene regulation. Here we describe a novel case of trans-interaction between alleles of the Malic enzyme (Men) locus in Drosophila melanogaster that results in allele-specific, non-additive gene expression. Using both empirical biochemical and predictive bioinformatic approaches, we show that the regulatory elements of one allele are capable of interacting in trans with, and modifying the expression of, the second allele. Furthermore, we show that nonlocal factors--different genetic backgrounds--are capable of significant interactions with individual Men alleles, suggesting that these trans-effects can be modified by both locally and distantly acting elements. In sum, these results emphasize the complexity of gene regulation and the need to understand both small- and large-scale interactions as more complete models of the role of trans-interactions in gene regulation are developed.