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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
Author(s) -
Kawano Mitsuoki,
Oshima Taku,
Kasai Hiroaki,
Mori Hirotada
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.03042.x
Subject(s) - biology , microbiology and biotechnology , rna , escherichia coli , messenger rna , transcription (linguistics) , gene , genetics , philosophy , linguistics
Summary 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.