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J. Bacteriol., Jan 1995, 401-412, Vol 177, No. 2
JE Houghton, TM Brown, AJ Appel, EJ Hughes and LN Ornston
The organization and transcriptional control of chromosomal cat genes
(required for dissimilation of catechol by the beta-ketoadipate pathway) in
the Pseudomonas putida biotype strain (ATCC 12633) are reported. Nucleotide
sequence reveals that catR is separated by 135 bp from the divergently
transcribed catBC,A; catC begins 21 nucleotides downstream from catB, and
catA begins 41 nucleotides downstream from catC. This contrasts with the
gene arrangement in other bacteria, in which catA lies several kilobases
upstream from catB. Properties of Tn5 mutants confirmed earlier suggestions
that catR is a transcriptional activator and indicated that catA is
activated by CatR independently of its activation of catBC. CatR binds to
both a DNA fragment containing the catR-catB intergenic region and another
DNA fragment containing catC. Pseudomonas strain RB1 resembles P. putida in
some respects. Divergence of the two Pseudomonas chromosomes was revealed
as nucleotide substitution of about 10% after alignment of known portions
of catR,BC,A. Divergent transcriptional controls are suggested by a cluster
of nucleotide sequence modifications in Pseudomonas strain RB1 which
disrupt a stem-loop structure directly upstream of catB in the P. putida
chromosome. Abrupt divergence of the catR,BC,A nucleotide sequences was
achieved during evolution by insertion of an 85-bp palindromic genetic
element uniquely positioned downstream from P. putida catR and
counterpoised by insertion of a similar palindromic sequence in the
Pseudomonas strain RB1 catB-catC intergenic region. Properties of the
palindromic genetic element suggest that it may serve functions analogous
to those of repetitive extragenic palindromic sequences and enteric
repetitive intergenic consensus sequences in enteric bacteria.
Copyright © 1995, American Society for Microbiology
Discontinuities in the evolution of Pseudomonas putida cat genes
Department of Biology, Georgia State University, Atlanta 30303.
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