Evolution of Intradiol Dioxygenase Genes in Bacteria

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The research program is designed to explore how the properties of genes and the stability of regions within genes are influenced by neighboring DNA sequences. Bacterial intradiol dioxygenase genes, the subjects of the investigation, share common ancestry and have undergone numerous rearrangements during their evolutionary divergence. Rearrangements might be expected to lead to the physical separation of independently transcribed genes, but the chromosomal position of divergent oxygenase genes has been conserved within different supraoperonic clusters. Selective forces favoring the clustering of genes will be explored by examining the physiological and genetic consequences of directed transposition of oxygenase genes from one cluster to another. Transposition can lead to genetic instability, and a possible source of instability is sequence-directed mutation, a process that can lead to deletions between regions of DNA sequence repetition. The extent to which sequence-directed mutations occur will be explored by comparison of the DNA sequences of genes that have undergone spontaneous mutation either in their normal location or after transposition to a different cluster. Processes that lead to sequence-directed mutation also might contribute to genetic repair, and this possibility will be explored by analysis of DNA sequence of mutations that revert readily. Enzymatic activation of oxygen is a fundamental biological process, and the genetic analysis of oxygenases will increase our understanding of biochemical steps that direct the assimilation of molecular oxygen into organic substrates. We plan to isolate mutant oxygenases that are functional but altered in substrate specificity or in catalytic efficiency,. Analysis of these proteins is likely to provide novel insight into interactions between oxygenases and their substrates.