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Proteolysis of CIII by HflB. The top panels show the band corresponding to CIII on a 17.5% SDS-PAGE, in the presence or absence of ATP (5 mM). A densitometric scan of the above gels showing the amount of CIII (2 nmol) remaining after treatment with HflB (0.04 nmol) is shown in the bottom panel. Lane U, undigested CIII; lanes 1 to 7, CIII treated with HflB for 5, 10, 20, 30, 40, 60, and 80 min.

Proteolysis of CIII by HflB. The top panels show the band corresponding to CIII on a 17.5% SDS-PAGE, in the presence or absence of ATP (5 mM). A densitometric scan of the above gels showing the amount of CIII (2 nmol) remaining after treatment with HflB (0.04 nmol) is shown in the bottom panel. Lane U, undigested CIII; lanes 1 to 7, CIII treated with HflB for 5, 10, 20, 30, 40, 60, and 80 min.

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The CIII protein encoded by the temperate coliphage lambda acts as an inhibitor of the ubiquitous Escherichia coli metalloprotease HflB (FtsH). This inhibition results in the stabilization of transcription factor λCII, thereby helping the phage to lysogenize the host bacterium. λCIII, a small (54-residue) protein of unknown structure, also protects...

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... A strong association with a two-pore potassium channel plays its role in bacterial survival and invasion by both sustaining intracellular homeostasis and modulating the secretion of effectors by type III secretion systems [45]. The lamda phage-encoded CIII protein serves as an inhibitor of the FtsH protease, thereby assisting the phage in its propagation during the lytic lifecycle [46]. At the same time, FtsH proteolytic activity may also hydrolyze the MgtC virulence protein essential for successful proliferation in macrophages [47]; therefore, the inhibition of FtsH could promote the normal course of systemic infections. ...
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... The expression of cro then began to suppress lacZ expression after pRM promoter (Additional file 1: Table S1) via binding to its binding site [25]. Additionally, cro expression has been shown to be strengthened by cII expression, which is inhibited to a degree because cII expression is still suppressed by endogenous Ftsh gene expression [26]. On the other hand, fermentation of lactose by the gut microbiota has been demonstrated to produce lactic acid and other short-chain fatty acids, leading to a pH drop within the colon, which would weaken patp2 and inhibit cI expression. ...
... Hence, ompA-lldD expression would gradually recover to a normal condition, producing a signal peptide [27], and L-LDH [28,29] would be translocated to the cell membrane to convert lactic acid to pyruvate in the periplasm. Additionally, the gradual recovery of cIII expression would unsuppress cII expression by inhibiting endogenous expression of Ftsh [26]. Unsuppressed cII expression would then strengthen cro expression, thus accelerating the inhibition of lacZ expression. ...
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... Kobiler et al. (2007) also suggested that oligomerization of cIII is required for its function as the HflB inhibitor. However, Halder et al. (2007) proposed that the cIII protein exists as a dimer under native conditions. Apart from the regulatory factors influencing the lysis-versuslysogenization decision known for many years, perhaps surprisingly, it is still possible to discover novel players in this game. ...
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... replicon that can exist either as a plasmid or integrated No gpC analogue in P22 gpNu3 gpNu3 gp8 gp8 Monomer/dimer/tetramer for gp8; monomer/dimer for gpNu3 gpB gpE gp1 gp5 Seen in reconstructions a gpNu3 gpB gp8 gp1 Scaffolds required for portal assembly into procapsid gp8 gp5 Scaffold-coat interaction not studied for l gpD gpD Dec Dec Both trimers; bind slightly different sites. a Note that P22 has no Dec, but its very close relative phage L does and L Dec binds to P22 capsids gpE gpE gp5 gp5 Both make icosahedral T¼7 head shells a gpU gpU No analogue in P22 gpD gpE Dec gp5 Dec is more discriminatory than D, i.e., unlike D, Dec does not occupy all of the quasiequivalent local threefold positions on the shell gp4 gp5 Unkown in l gp4 gp10 No gp10 analogue in l (but see gpFII above) gp4 gp9 No gp9 analogue in l (but see Stf below?) gp10 gp9 No gp9 analogue in l (but see Stf below?) gp10 gp10 No gp10 analogue in l (but see gpFII above) gp10 gp26 No gp10 or gp26 (?) analogue in l Xis? Xis Xis Monomer in l, but binds cooperatively so could interact on DNA (Abbani et al., 2007); multimer in P22 CIII CIII C3 C3 C3 is homologue of l CIII; l CIII is dimer (Halder et al., 2007); P22 interaction by homology with l CIII Cro Cro Cro Cro Both homodimers gpRz gpRz1 gp15 gp15 Predicted for P22 by homology a Not recognizably similar in amino acid sequence but very likely ancient homologues. ...
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... Other factors such as λCIII and the host hfl proteins that influence the lysis-lysogeny switching affect the stability of CII in one way or the other. λCIII promotes lysogeny by acting as a general inhibitor of E. coli HflB that degrades CII [16]. ...
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... No homologues are known from Archaea, and only six from Bacteria, including three from Family I75 contains the bacteriophage lambda CIII protein, which has been shown to be an inhibitor of the metalloendopeptidase FtsH (family M41). Degradation of the phage CII protein by FtsH pushes the phage towards lysis rather than lysogeny, so inhibition of FtsH retains the phage in the lysogenic state [111]. Homologues are known from E. coli and Salmonella enterica (Enterobacteriaceae). ...
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... Bacteriophages have two alternative modes of development, a quiescent phase where the phage genome is incorporated into the host genome (lysogeny) and a lytic phase, where phage particles are released from the infected cell. The host peptidase FtsH (M41.001) pushes the phage towards lysis by degrading the phage protein CII, and by inhibiting FtsH with CIII, the phage can persist in the lysogenic stage [59]. ...
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... The mutant cII genes were subcloned into pET15b at the NdeI and BamHI sites, to change the antibiotic selection marker from kanamycin to ampicillin. The resulting plasmids were derivatives of pAB412 (Halder et al., 2007) which carries the wild-type cII gene (Supplementary Fig. S3c). ...
... Complementation assays. The in vivo activity of His 6 -tagged native and mutant CII was tested by complementation assays following the method described by Halder et al. (2007), as described below. E. coli BL21 (DE3) cells containing pAB412 (carrying the native cII gene) or any of the plasmids pKP301 to pKP306 (carrying one of the mutated cII genes, see Supplementary Table S1) were used as hosts. ...
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The CII protein of the temperate bacteriophage lambda is the decision-making factor that determines the viral lytic/lysogenic choice. It is a homotetrameric transcription activator that recognizes and binds specific direct repeat sequences TTGCN(6)TTGC in the lambda genome. The quaternary structure of CII is held by a four-helix bundle. It is known that the tetrameric organization of CII is necessary for its activity, but the molecular mechanism behind this requirement is not known. By specific site-directed mutagenesis of hydrophobic residues in the alpha4 helix of CII that constitutes the four-helix bundle, we found that residues leu70, val74 and leu78 were crucial for maintaining the tetrameric structure of the protein. When any of these residues was substituted by a polar one, CII lost its activity and failed to promote lysogeny. This loss of activity was accompanied by the inability of CII to form tetramers, to bind DNA or to activate transcription.