COMPARISON OF THE NUCLEOTIDE-SEQUENCES OF THE META-CLEAVAGE PATHWAY GENES OF TOL PLASMID PWW0 FROM PSEUDOMONAS-PUTIDA WITH OTHER META-CLEAVAGE GENES SUGGESTS THAT BOTH SINGLE AND MULTIPLE NUCLEOTIDE SUBSTITUTIONS CONTRIBUTE TO ENZYME EVOLUTION
S. Harayama et M. Rekik, COMPARISON OF THE NUCLEOTIDE-SEQUENCES OF THE META-CLEAVAGE PATHWAY GENES OF TOL PLASMID PWW0 FROM PSEUDOMONAS-PUTIDA WITH OTHER META-CLEAVAGE GENES SUGGESTS THAT BOTH SINGLE AND MULTIPLE NUCLEOTIDE SUBSTITUTIONS CONTRIBUTE TO ENZYME EVOLUTION, MGG. Molecular & general genetics, 239(1-2), 1993, pp. 81-89
TOL plasmid pWW0 from Pseudomonas putida mt-2 encodes catabolic enzyme
s required for the oxidation of toluene and xylenes. The structural ge
nes for these catabolic enzymes are clustered into two operons, the xy
lCM ABN operon, which encodes a set of enzymes required for the transf
ormation of toluene/xylenes to benzoate/toluates, and the xylXYZLTEGFJ
QKIH operon, which encodes a set of enzymes required for the transform
ation of benzoate/toluates to Krebs cycle intermediates. The latter op
eron can be divided physically and functionally into two parts, the xy
lXYZL cluster, which is involved in the transformation of benzoate/tol
uates to (methyl)catechols, and the xylTEGFJQKIH cluster, which is inv
olved in the transformation of (methyl)catechols to Krebs cycle interm
ediates. Genes isofunctional to xylXYZL are present in Acinetobacter c
alcoaceticus, and constitute a benzoate-degradative pathway, while xyl
TEGFJQKIH homologous encoding enzymes of a methylphenol-degradative pa
thway and a naphthalene-degradative pathway are present on plasmid pVI
150 from P. putida CF600, and on plasmid NAH7 from P. putida PpG7, res
pectively. Comparison of the nucleotide sequences of the xylXYZLTEGFJQ
KIH genes with other isofunctional genes suggested that the xylTEGFJQK
IH genes on the TOL plasmid diverged from these homologues 20 to 50 mi
llion years ago, while the xylXYZL genes diverged from the A. calcoace
ticus homologues 100 to 200 million years ago. In codons where amino a
cids are not conserved, the substitution rate in the third base was hi
gher than that in synonymous codons. This result was interpreted as in
dicating that both single and multiple nucleotide substitutions contri
buted to the amino acid-substituting mutations, and hence to enzyme ev
olution. This observation seems to be general because mammalian globin
genes exhibit the same tendency.