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Vol. 180, Issue 13, 3295-3303, July 1, 1998
1 Departments of
Microbiology1 and
2 Biochemistry,2 University of Illinois,
Urbana, Illinois 61801
The genes encoding several key fatty acid biosynthetic enzymes
(called the fab cluster) are clustered in the order
plsX-fabH-fabD-fabG-acpP-fabF at min 24 of the
Escherichia coli chromosome. A difficulty in analysis of
the fab cluster by the polar allele duplication approach (Y. Zhang and J. E. Cronan, Jr., J. Bacteriol. 178:3614-3620, 1996) is that several of these genes are essential for the growth of
E. coli. We overcame this complication by use of the
fab gene cluster of Salmonella typhimurium, a
close relative of E. coli, to provide functions necessary
for growth. The S. typhimurium fab cluster was isolated by
complementation of an E. coli fabD mutant and was found to
encode proteins with >94% homology to those of E. coli.
However, the S. typhimurium sequences cannot recombine with
the E. coli sequences required to direct polar allele
duplication via homologous recombination. Using this approach, we found
that although approximately 60% of the plsX transcripts initiate at promoters located far upstream and include the upstream rpmF ribosomal protein gene, a promoter located upstream of
the plsX coding sequence (probably within the upstream
gene, rpmF) is sufficient for normal growth. We have also
found that the fabG gene is obligatorily cotranscribed with
upstream genes. Insertion of a transcription terminator cassette
(
Transcriptional Analysis of Essential Genes of the
Escherichia coli Fatty Acid Biosynthesis Gene Cluster by
Functional Replacement with the Analogous Salmonella
typhimurium Gene Cluster
-Cm cassette) between the fabD and fabG
genes of the E. coli chromosome abolished fabG transcription and blocked cell growth, thus providing the first indication that fabG is an essential gene. Insertion of the
-Cm cassette between fabH and fabD caused
greatly decreased transcription of the fabD and
fabG genes and slower cellular growth, indicating that
fabD has only a weak promoter(s).
Copyright © 1998 by American Society for Microbiology
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