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J. Bacteriol., Nov 1995, 6644-6651, Vol 177, No. 22
DD Jaworski and DB Clewell
The origin of transfer (oriT) of the 18-kb conjugative transposon Tn916 has
been localized to a 466-bp region which spans nucleotides 15215 to 15681 on
the transposon map. The oriT lies within an intercistronic region between
open reading frames ORF20 and ORF21 that contains six sets of inverted
repeats ranging from 10 to 20 bp in size. The segment contains three
sequences showing identity in 9 of 12 bp to the consensus nicking site
(nic) of the IncP family of conjugative plasmids found in gram-negative
bacteria. Overlapping one of these sequences is a region similar to the nic
site of the F plasmid. Functionality was based on the ability of the
oriT-containing sequence to provide a cis- acting mobilization of chimeras
involving the shuttle vector pWM401 in response to activation in trans by
an intact chromosome-borne transposon Tn916 delta E. Cloned segments of 466
or 376 nucleotides resulted in unselected cotransfer of the plasmid at
levels of about 40% when selection was for Tn916 delta E, whereas a 110-bp
segment resulted in cotransfer at a frequency of about 7%. Mobilization was
specific in that gram-positive plasmids, such as pAD1 and pAM beta 1, and
the gram- negative plasmids pOX38 (a derivative of F) and RP1 did not
mobilize oriT-containing chimeras.
Copyright © 1995, American Society for Microbiology
A functional origin of transfer (oriT) on the conjugative transposon Tn916
Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109, USA.
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