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Journal of Bacteriology, November 1998, p. 5697-5703, Vol. 180, No. 21
Department of Molecular and Cell Biology,
University of California, Berkeley, California 94720-3204
Received 22 June 1998/Accepted 26 August 1998
Myxococcus xanthus is a gram-negative bacterium which
has a complex life cycle. Autochemotaxis, a process whereby cells
release a self-generated signaling molecule, may be the principal
mechanism facilitating directed motility in both the vegetative
swarming and developmental aggregation stages of this life cycle. The
process requires the Frz signal transduction system, including FrzZ, a protein which is composed of two domains, both showing homology to the
enteric chemotaxis response regulator CheY. The first domain of FrzZ
(FrzZ1), when expressed as bait in the yeast two-hybrid system and
screened against a library, was shown to potentially interact with the C-terminal portion of a protein encoding an ATP-binding cassette (AbcA). The activation domain-AbcA
fusion protein did not interact with the second domain of FrzZ (FrzZ2) or with two other M. xanthus response
regulator-containing proteins presented as bait, suggesting that the
FrzZ1-AbcA interaction may be specific. Cloning and sequencing of the
upstream region of the abcA gene showed the ATP-binding
cassette to be linked to a large hydrophobic, potentially
membrane-spanning domain. This domain organization is
characteristic of a subgroup of ABC transporters which perform export
functions. Cloning and sequencing downstream of abcA
indicated that the ABC transporter is at the start of an operon
containing three open reading frames. An insertion mutation in the
abcA gene resulted in cells displaying the frizzy aggregation phenotype, providing additional evidence that FrzZ and AbcA
may be part of the same signal transduction pathway. Cells with
mutations in genes downstream of abcA showed no
developmental defects. Analysis of the proposed exporter role of AbcA
in cell mixing experiments showed that the ABC transporter mutant could be rescued by extracellular complementation. We speculate that the
AbcA protein may be involved in the export of a molecule required for
the autochemotactic process.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
An ABC Transporter Plays a Developmental
Aggregation Role in Myxococcus xanthus
*
Corresponding author. Mailing address: Department of
Molecular and Cell Biology, University of California, Berkeley, CA
94720-3204. Phone: (510) 642-2293. Fax: (510) 642-7000. E-mail:
zusman{at}uclink4.berkeley.edu.
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