My. Peredelchuk et Gn. Bennett, A METHOD FOR CONSTRUCTION OF ESCHERICHIA-COLI STRAINS WITH MULTIPLE DNA INSERTIONS IN THE CHROMOSOME, Gene, 187(2), 1997, pp. 231-238
A system for construction of E. coli strains with multiple DNA inserti
ons in the chromosome, based on elements of modules for site specific
recombination of Tn1545 and phage lambda, has been developed. Circular
non-replicating DNA fragments containing the transposon attachment si
te (attTn), an excisable cassette with a selectable marker, and a gene
of interest integrate randomly into the chromosome of a host E. coli
strain when provided with transposon integrase, Int-Tn (the host strai
n was obtained by insertion of the fragment containing transposon int-
Tn gene coding for Int-Tn into the chromosome). Integration of these f
ragments into the chromosome of int-Tn(+). cells gives rise to a colle
ction of antibiotic-resistant clones with single insertions at differe
nt locations in the chromosome. These insertions are transferred subse
quently by P1 transduction into one strain and selected for antibiotic
resistance provided by the cassette with the selectable marker. After
transduction of each copy, a helper plasmid bearing phage lambda. xis
and int genes is introduced into the cells to excise the drug resista
nce gene flanked with the lambda attL and lambda attR sites from the c
hromosome. Cells cured of the helper plasmid can undergo the next cycl
e of P1 transduction/drug resistance gene excision. Each cycle adds an
other chromosomal copy of the foreign gene. To show the utility of the
system, we constructed an E. coli strain bearing several chromosomal
copies of lacZ at different locations.