DNA Sequences of Genes Encoding Acinetobacter calcoaceticus Protocatechuate 3,4-Dioxygenase: Evidence Indicating Shuffling of Genes and of DNA Sequences within Genes during Their Evolutionary Divergence

摘要

The DNA sequence of a 2.391-base-pair HindIII restriction fragment ofAcinetobacter calcoaceticus DNA containing the pcaCHG genes is reported. The DNA sequence reveals that A. calcoaceticus pca genes, encoding enzymes required for portocatechuate metabolism, are arranged in a single transcriptional unit, pcaEFDBCHG, whereas homologous genes are arranged differently in Pseudomonas putida. The pcaG and pcaH genes represent separate reading frames respectively encoding the alpha and beta subunits of protocatechuate 3,4-dioxygenase (EC1.13.1.3); previously a single designation, pcaA, had been used to represent DNA encoding this enzyme. The alpha and beta protein subunits appear to share common ancestry with each other and with catechol 1,2-dioxygenases from A. calcoaceticus and P. putida. Marked conservation of amino acid sequence is observed in a region containing two histidyl residues and two tyrosyl residues that appear to ligate iron within each oxygenase. In some regions within the aligned oxygenase sequences, DNA sequences appear to be conserved at a level beyond the extent that might have been demanded by selection at the level of protein. Reprints. (jes)