ID   CCDB3_ECOLX             Reviewed;         101 AA.
AC   Q52042;
DT   01-NOV-1997, integrated into UniProtKB/Swiss-Prot.
DT   21-SEP-2011, sequence version 2.
DT   25-MAY-2022, entry version 98.
DE   RecName: Full=Toxin CcdB;
DE   AltName: Full=Cytotoxic protein CcdB;
DE   AltName: Full=Protein LetD;
GN   Name=ccdB; Synonyms=letB;
OS   Escherichia coli.
OG   Plasmid pKIL18.
OC   Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacterales;
OC   Enterobacteriaceae; Escherichia.
OX   NCBI_TaxID=562;
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RX   PubMed=7926841; DOI=10.1016/0378-1119(94)90235-6;
RA   Bernard P., Gabant P., Bahassi E.M., Couturier M.;
RT   "Positive-selection vectors using the F plasmid ccdB killer gene.";
RL   Gene 148:71-74(1994).
CC   -!- FUNCTION: Toxic component of a type II toxin-antitoxin (TA) system,
CC       functioning in plasmid maintainence. Responsible for the post-
CC       segregational killing (PSK) of plasmid-free cells, also referred to as
CC       a plasmid addiction system. Half-life of over 2 hours. Interferes with
CC       the activity of DNA gyrase, inducing it to form a covalent GyrA-DNA
CC       complex that cannot be resolved, thus promoting breakage of plasmid and
CC       chromosomal DNA. Toxicity is inhibited by labile antitoxin CcdA, which
CC       blocks the activity of CcdB; CcdA also removes bound CcdB protein from
CC       the CcdB-GyrA complex by forming a CcdA-CcdB complex, a process termed
CC       rejuvenation. Functions as a transcriptional corepressor for the ccdAB
CC       operon, repression also requires CcdA (By similarity). {ECO:0000250}.
CC   -!- SUBUNIT: Homodimer. Forms a complex with GyrA, probably a tetramer
CC       GyrA(2)CcdB(2), in which GyrA is inactive. Forms a complex with toxin
CC       CcdB; the CcdA-CcdB(2) trimer is sufficient for rejuvenation, whereas
CC       maximal operon repression occurs with CcdA(2)CcdB(2) (By similarity).
CC       {ECO:0000250}.
CC   -!- SIMILARITY: Belongs to the CcdB toxin family. {ECO:0000305}.
CC   -!- SEQUENCE CAUTION:
CC       Sequence=AAA98268.1; Type=Erroneous initiation; Note=Extended N-terminus.; Evidence={ECO:0000305};
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DR   EMBL; L27083; AAA98268.1; ALT_INIT; Genomic_DNA.
DR   RefSeq; WP_001159868.1; NZ_WWEV01000072.1.
DR   RefSeq; YP_003108267.1; NC_013122.1.
DR   AlphaFoldDB; Q52042; -.
DR   SMR; Q52042; -.
DR   OrthoDB; 2075946at2; -.
DR   GO; GO:0008657; F:DNA topoisomerase type II (double strand cut, ATP-hydrolyzing) inhibitor activity; IEA:InterPro.
DR   GO; GO:0006276; P:plasmid maintenance; IEA:InterPro.
DR   Gene3D; 2.30.30.110; -; 1.
DR   InterPro; IPR002712; CcdB.
DR   InterPro; IPR011067; Plasmid_toxin/cell-grow_inhib.
DR   Pfam; PF01845; CcdB; 1.
PE   3: Inferred from homology;
KW   Plasmid; Repressor; Toxin-antitoxin system; Transcription;
KW   Transcription regulation.
FT   CHAIN           1..101
FT                   /note="Toxin CcdB"
FT                   /id="PRO_0000068389"
SQ   SEQUENCE   101 AA;  11707 MW;  566AF6681DFE94FE CRC64;
     MQFKVYTYKR ESRYRLFVDV QSDIIDTPGR RMVIPLASAR LLSDKVSREL YPVVHIGDES
     WRMMTTDMAS VPVSVIGEEV ADLSHRENDI KNAINLMFWG I