Previous Article | Next Article ![]()
J. Bacteriol., 10 1997, 6228-6237, Vol 179, No. 20
AJ Link, D Phillips and GM Church
We have developed a new system of chromosomal mutagenesis in order to study
the functions of uncharacterized open reading frames (ORFs) in wild-type
Escherichia coli. Because of the operon structure of this organism,
traditional methods such as insertional mutagenesis run the risk of
introducing polar effects on downstream genes or creating secondary
mutations elsewhere in the genome. Our system uses crossover PCR to create
in-frame, tagged deletions in chromosomal DNA. These deletions are placed
in the E. coli chromosome by using plasmid pKO3, a gene replacement vector
that contains a temperature-sensitive origin of replication and markers for
positive and negative selection for chromosomal integration and excision.
Using kanamycin resistance (Kn(r)) insertional alleles of the essential
genes pepM and rpsB cloned into the replacement vector, we calibrated the
system for the expected results when essential genes are deleted. Two
poorly understood genes, hdeA and yjbJ, encoding highly abundant proteins
were selected as targets for this approach. When the system was used to
replace chromosomal hdeA with insertional alleles, we observed vastly
different results that were dependent on the exact nature of the
insertions. When a Kn(r) gene was inserted into hdeA at two different
locations and orientations, both essential and nonessential phenotypes were
seen. Using PCR-generated deletions, we were able to make in-frame deletion
strains of both hdeA and yjbJ. The two genes proved to be nonessential in
both rich and glucose-minimal media. In competition experiments using
isogenic strains, the strain with the insertional allele of yjbJ showed
growth rates different from those of the strain with the deletion allele of
yjbJ. These results illustrate that in-frame, unmarked deletions are among
the most reliable types of mutations available for wild-type E. coli.
Because these strains are isogenic with the exception of their deleted
ORFs, they may be used in competition with one another to reveal phenotypes
not apparent when cultured singly.
Copyright © 1997, American Society for Microbiology
Methods for generating precise deletions and insertions in the genome of wild-type Escherichia coli: application to open reading frame characterization
Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»