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.
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 (approximately 370 nucleotides) encoding LdrD and an unstable cis-encoded antisense RNA (approximately 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 pre-sent on any known plasmids but are conserved in Salmonella and other enterobacterial species.
Research and Education Center for Genetic Information, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
Mitsuoki
M
Kawano
Taku
T
Oshima
Hiroaki
H
Kasai
Hirotada
H
Mori
D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000235:genetics*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics*; D004755:Enterobacteriaceae / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family; D015388:Organelles / Q000648:ultrastructure; D014176:Protein Biosynthesis; D011815:R Factors / Q000235:genetics; D016372:RNA, Antisense / Q000235:genetics / Q000502:physiology; D012329:RNA, Bacterial / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D020080:Tandem Repeat Sequences
D001427:Bacterial Toxins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C465558:LdrD protein, E coli; D016372:RNA, Antisense; D012329:RNA, Bacterial; D012333:RNA, Messenger