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J. Bacteriol. doi:10.1128/JB.01403-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Characterization of the variants, flanking genes and promoter activity of Leifsonia xyli subsp. cynodontis insertion sequence IS1237

State Key Laboratory of Virology, Department of Biochemistry and Molecular Biology, College of Life Sciences, Wuhan University, Hubei 430072, China

^* To whom correspondence should be addressed. Email: TaiyuanL{at}hotmail.com. yizhang{at}whu.edu.cn.

	Abstract

This study presented a comprehensive study of the distribution and function of an insertion sequence (IS) element, IS1237, in the genome of Leifsonia xyli subsp. cynodontis, a useful genetic carrier to express beneficial foreign genes in plants. Two shorter IS1237 isoforms, IS1237d1 and IS1237d2 resulted from precise deletion between two non-perfect repeats, were found in the bacterial genome at 1/5 of the wild-type IS1237. Both the genome and native plasmid pCXC100 harbor a truncated toxin-antitoxin cassette being precisely fused with a 5'-truncated IS1237 at one non-perfect repeat, indicating a hot site for DNA rearrangement. Nevertheless, no transposition activity was detected when the putative transposase of IS1237 was overexpressed in E. coli. TAIL-PCR identified 13 upstream and 10 downstream unique flanking sequences, and two pairs of them are from the same loci, suggesting that IS1237 has up to 65 unique loci in the L. xyli subsp. cynodontis chromosome. The presence of TAA or TTA direct repeat sequences at most insertion sites indicated that IS1237 inserts into these loci by active transposition. IS1237 showed a high propensity to insert into other IS elements, such as the identified ISLxc1 and ISLxc2, which could offer IS1237 a non-autonomous transposition pathway through its host IS elements. Interestingly, we showed that IS1237 harbors a strong promoter at the 3' end and a weak one at the 5' end, and both promoters promote the transcription of adjacent genes in different gram-positive bacteria. The high copy number nature of IS1237 and its promoter activity may contribute to bacterial fitness.