J. Bacteriol., 01 1997, 1-8, Vol 179, No. 1
K Cho, C Fuqua and SC Winans
By screening for octopine-inducible gene expression, we previously
identified all the genes required for utilization of octopine as a source
of carbon, nitrogen, and energy. They are (i) octopine oxidase, which
converts octopine to arginine and pyruvate and is encoded by the ooxAB
operon, (ii) arginase, which converts arginine to ornithine and urea and is
encoded by arcA, (iii) ornithine cyclodeaminase, which converts ornithine
to proline and ammonia and is encoded by the homologous arcB and ocd genes,
and (iv) proline dehydrogenase, which converts proline to glutamate and is
encoded by putA. Here we describe the regulation and localization of each
of these genes. The ooxA-ooxB- ocd operon was previously shown to reside on
the Ti plasmid and to be directly inducible by octopine. The arcAB operon
is directly inducible by arginine, while it is induced by octopine only in
strains that can convert octopine to arginine. Ornithine may also be a
direct inducer of arcAB. putA is directly inducible by proline, while
induction by octopine and by arginine (and probably by ornithine) requires
their conversion to proline. Genetic studies indicate that arcAB and putA
are localized on a conjugal genetic element. This element can be
transferred to other Agrobacterium tumefaciens strains by a mechanism that
does not require recA-dependent homologous recombination. Transfer of this
genetic element from A. tumefaciens R10 requires at least one tra gene
found on its Ti plasmid, indicating that this element is not
self-transmissible but is mobilizable by the Ti plasmid. The DNA containing
the arcAB and putA genes comigrates with a 243-kb linear molecular weight
standard on field inversion electrophoretic gels.
Copyright © 1997, American Society for Microbiology
Transcriptional regulation and locations of Agrobacterium tumefaciens genes required for complete catabolism of octopine
Section of Microbiology, Cornell University, Ithaca, New York 14853, USA.
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