Si. Sato et al., IDENTIFICATION AND CHARACTERIZATION OF GENES ENCODING CARBAZOLE 1,9A-DIOXYGENASE IN PSEUDOMONAS SP STRAIN CA10, Journal of bacteriology, 179(15), 1997, pp. 4850-4858
Nucleotide sequence analysis of the flanking regions of the carBC gene
s of Pseudomonas sp, strain CA10 revealed that there were two open rea
ding frames (ORFs) ORF4 and ORF5, in the upstream region of carBC, Sim
ilarly, three ORFs, ORF6 to ORF8, were found in the downstream region
of carBC, The deduced amino acid sequences of ORF6 and ORF8 showed hom
ologies with ferredoxin and ferredoxin reductase components of bacteri
al multicomponent dioxygenase systems, respectively, ORF4 and ORF5 had
the same sequence and were tandemly linked, Their deduced amino acid
sequences showed about 30% homology with large (alpha) subunits of oth
er terminal oxygenase components. Functional analysis using resting ce
lls harboring the deleted plasmids revealed that the products of ORF4
and -5, ORF6, and ORF8 were terminal dioxygenase, ferredoxin, and ferr
edoxin reductase, respectively, of carbazole 1,9a-dioxygenase (CARDO),
which attacks the angular position adjacent to the nitrogen atom of c
arbazole, and that the product of ORF7 is not indispensable for CARDO
activity, Based on the results, ORF4, ORF5, ORF6, and ORF8 were design
ated car Aa, carAa, carAc, and carAd, respectively, The products of ca
rAa, carAd, and ORF7 were shown by sodium dodecyl sulfate-polyacrylami
de gel electrophoresis to be polypeptides with molecular masses of 43,
36, and 11 kDa, respectively, However, the product of carAc was not d
etected in Escherichia coli, CARDO has the ability to oxidize a wide v
ariety of polyaromatic compounds, including dibenzo-p-dioxin, dibenzof
uran, biphenyl, and polycyclic aromatic hydrocarbons such as naphthale
ne and phenanthrene, Since 2,2',3-trihydroxydiphenyl ether and 2,2',3-
trihydroxybiphenyl were identified as metabolites of dibenzo-p-dioxin
and dibenzofuran, respectively, it was considered that CARDO attacked
at the angular position adjacent to the oxygen atom of dibenzo-p-dioxi
n and dibenzofuran as in the case with carbazole.