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Journal of Bacteriology, November 2001, p. 6444-6453, Vol. 183, No. 21
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.21.6444-6453.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Genetic Analysis of the Sinorhizobium
meliloti BacA Protein: Differential Effects of Mutations
on Phenotypes
Kristin
LeVier and
Graham C.
Walker*
Biology Department, Massachusetts Institute
of Technology, Cambridge, Massachusetts 02139
Received 22 May 2001/Accepted 10 August 2001
Sinorhizobium meliloti strains lacking BacA function
are impaired in symbiosis with alfalfa host plants and display altered sensitivities to a number of compounds relative to wild-type strains. With the goal of finding clues to the currently unknown biological function(s) of BacA, we carried out a genetic analysis to determine which amino acids are critical for protein function and to attempt to
ascertain whether the multiple phenotypes that result from a
bacA-null allele were the result of a common
cause or whether BacA has multiple functions. We have created a set of
20 site-directed mutants in which selected individual amino acids in
bacA were replaced with glycine residues. The resulting
mutants were characterized to determine how the various amino acid
changes affected a number of phenotypes associated with loss of BacA
function. Mutants H165G, W182G, D198G, and R284G had null phenotypes
for all functions assayed, while mutants W57G, S83G, S231G, and K350G
were indistinguishable from wild-type strains. The remaining 12 site-directed mutants demonstrate mixed phenotypic characteristics and
fall into a number of distinctly different groups. These observations
may be consistent with a role for BacA in multiple, nonoverlapping functions.
*
Corresponding author. Mailing address: Biology
Department, 68-659, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139. Phone: (617) 253-6716. Fax:
(617) 253-2643. E-mail: gwalker{at}mit.edu.
Journal of Bacteriology, November 2001, p. 6444-6453, Vol. 183, No. 21
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.21.6444-6453.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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