TOL plasmids encode enzymes responsible for utilization of toluene and related aromatic compounds by Pseudomonas putida, ultimately converting them to central metabolic intermediates. The nucleotide sequence for the 5.6 kb xylGFJQK region of the pDK1 TOL meta operon was determined. DNA sequence analysis revealed the presence of five open reading frames corresponding to xylG (1458 bp), xylF (846 bp), xylJ (783 bp), xylQ (936 bp) and xylK (1047 bp), encoding predicted protein products of 51.6, 31.3, 27.8, 32.8, and 36.6 kDa in size, respectively. The average G+C content of the xylLTEGFJQK region was 65.7%, somewhat higher than the 58.9% seen in the immediately upstream xylXYZ region and substantially more than the 50% G+C content reported for the upper TOL operon of this plasmid. Homology comparisons were made with genes and proteins of related catabolic plasmids. The dmpCDEFG and pWWO xylGFJQK regions exhibit consistently high levels of nucleotide and amino acid homology to pDK1 xylGFJQK throughout the entire region. In contrast, although the nucleotide sequence homology of the Acinetobacter atdCDE region to xylGFJ is high, the homology of atdFG to xylQK is markedly less. Such radical changes in homology between corresponding regions of different operons, combined with variable base and codon usage patterns within and between operons, provides additional support for the idea that the upper and lower operons encoding enzymes of aromatic pathways have evolved independently of one another and that these operons have continued to exchange genetic material with homologous expression units through a series of recombination events. Recombinant plasmids were constructed for individual expression of each of the xylGFJQK genes. HMSD (XylG) and HMSH (XylF) were partially purified and characterized with respect to substrate specificity and kinetic mechanism. Evidence was obtained suggesting that the HMSD reaction occurs via a steady state ordered mechanism or a random mechanism where binding of the first substrate effects the enzyme's affinity for the second substrate.
| Identifer | oai:union.ndltd.org:unt.edu/info:ark/67531/metadc2270 |
| Date | 12 1900 |
| Creators | Poulter, Melinda D. |
| Contributors | Benjamin, Robert C., Knesek, John, O'Donovan, Gerard A., Pirtle, Robert M., Zimmerman, Earl G. |
| Publisher | University of North Texas |
| Source Sets | University of North Texas |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Format | Text |
| Rights | Use restricted to UNT Community, Copyright, Poulter, Melinda D., Copyright is held by the author, unless otherwise noted. All rights reserved. |
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