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Journal of Bacteriology, April 2000, p. 1978-1986, Vol. 182, No. 7
Centre for Cellular and Molecular Biology,
Hyderabad 500 007, India
Received 17 September 1999/Accepted 12 January 2000
Null mutations in the Escherichia coli uup locus (at
21.8 min) serve to increase the frequency of RecA-independent precise excision of transposable elements such as Tn10 and to
reduce the plaque size of bacteriophage Mu (Uup
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Characterization of the uup Locus and
Its Role in Transposon Excisions and Tandem Repeat Deletions in
Escherichia coli
phenotype). By the combined approaches of physical mapping of the
mutations, complementation analyses, and protein overexpression from
cloned gene fragments, we have demonstrated in this study that the
Uup
phenotype is the consequence of the absence of
expression of the downstream gene (uup) of a two-gene
operon, caused either directly by insertions in uup or
indirectly by the polar effect of insertions in the upstream gene
(ycbY). The promoter for uup was mapped
upstream of ycbY by primer extension analysis on cellular RNA, and assays of reporter gene expression indicated that it is a
moderately active, constitutive promoter. The uup mutations were also shown to increase, in a RecA-independent manner, the frequencies of nearly precise excision of Tn10 derivatives
and of the deletion of one copy of a chromosomal tandem repeat,
suggesting the existence of a shared step or intermediate in the
pathways of these latter events and that of precise excision. Finally, we found that mutations that increase the frequency of precise excision
of Tn10 are divisible into two categories, depending upon
whether they did (uup, ssb, polA,
and topA) or did not (mutHLS, dam,
and uvrD) also increase precise excision frequency of the mini-Tn10 derivatives. It is suggested that the
differential response of mini-Tn10 and Tn10 to
the second category of mutations is related to the presence,
respectively, of perfect and of imperfect terminal inverted repeats in them.
*
Corresponding author. Mailing address: Centre for
Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India.
Phone: 91-40-7172241. Fax: 91-40-7171195. E-mail:
shankar{at}ccmb.ap.nic.in.
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