Molecular characterization of long direct repeat (LDR) sequences expressing a stable mRNA encoding for a 35-amino-acid cell-killing peptide and a cis-encoded small antisense RNA in Escherichia coli
Article first published online: 18 JUL 2002
Volume 45, Issue 2, pages 333–349, July 2002
How to Cite
Kawano, M., Oshima, T., Kasai, H. and Mori, H. (2002), Molecular characterization of long direct repeat (LDR) sequences expressing a stable mRNA encoding for a 35-amino-acid cell-killing peptide and a cis-encoded small antisense RNA in Escherichia coli. Molecular Microbiology, 45: 333–349. doi: 10.1046/j.1365-2958.2002.03042.x
- Issue published online: 18 JUL 2002
- Article first published online: 18 JUL 2002
Genome sequence analyses of Escherichia coli K-12 revealed four copies of long repetitive elements. These sequences are designated as long direct repeat (LDR) sequences. Three of the repeats (LDR-A, -B, -C), each approximately 500 bp in length, are located as tandem repeats at 27.4 min on the genetic map. Another copy (LDR-D), 450 bp in length and nearly identical to LDR-A, -B and -C, is located at 79.7 min, a position that is directly opposite the position of LDR-A, -B and -C. In this study, we demonstrate that LDR-D encodes a 35-amino-acid peptide, LdrD, the overexpression of which causes rapid cell killing and nucleoid condensation of the host cell. Northern blot and primer extension analysis showed constitutive transcription of a stable mRNA (≈ 370 nucleotides) encoding LdrD and an unstable cis-encoded antisense RNA (≈ 60 nucleotides), which functions as a trans-acting regulator of ldrD translation. We propose that LDR encodes a toxin–antitoxin module. LDR-homologous sequences are not present on any known plasmids but are conserved in Salmonella and other enterobacterial species.