Table 1 Plaque selleckchem morphology upon infection with λcIII 67 Genotype of host E. coli cell Plaque morphology Wild Type Clear Wild Type + pQKC Turbid AK990 (ΔhflKC::Kan) Turbid Is it then possible that enhancement of lysogeny can occur through a different mechanism that does not involve the stabilization of CII? Increase in lambda lysogeny is invariably

linked to the stability of CII in all published reports to date. Can the two phenomena be delinked in some special case such as a ΔhflKC host? We tested this possibility by measuring the stability of cloned CII in wild type and ΔhflKC cells, both infected with λcIII 67 . A greater stabilization of CII GSK1210151A occurred in ΔhflKC cells (Figure 4). Therefore, an increase in the lysogenic frequency indeed requires the stabilization of CII. Figure 4 Effect of infection by cIII -mutant lambda on in vivo proteolysis of CII. The proteolysis of CII was visualized in wild type (open circles) or AK990 (diamonds) cells infected with λcIII 67 . The expression of CII was induced with IPTG, and the cells

were infected with the phage after 20 minutes. Protein synthesis was stopped 25 minutes later with spectinomycin. The relative amount of CII was measured at regular intervals by western blotting followed by quantification using densitometric analysis. This enhanced stabilization of CII is observed only under conditions of phage infection, even when CIII is nonfunctional. Therefore in addition PND-1186 chemical structure to CIII, there could be another as yet unidentified factor in λ that increases the stability of CII and hence, promotes lysogeny (see Figure 5A). The presence of such a CII-stabilizing factor (CSF) can only be demonstrated in HflKC-deleted

cells. Therefore, the activities of CSF and HflKC must have some connections (Figure 5B). Likewise, CIII and HflKC are likely to be connected as well. The different outcomes for deletion or overexpression of hflKC on lysogeny as well as on the stability of CII under various conditions are summarized in Figure 5A. Figure 5 The effect of deletion or overexpression of hflKC on λ lysogeny and on the stability of CII: A summary of results and possible mechanisms. (A) A summary of results published previously as well as reported in this study is shown schematically. Some unanswered questions that remain Ribonucleotide reductase are highlighted in the boxes. (B) Mechanisms for the stability of CII and the lysogenic outcome under various conditions are shown. HflB acts upon CII to digest CII, as indicated by the arrow. This digestion is inhibited by HflKC, by CIII or by the postulated CII-stabilizing factor CSF. The levels of inhibition are denoted by the lengths of the blunt lines. Possible crosstalk between HflKC and CIII or CSF are indicated by curved arrows. Dashed arrows denote lack of crosstalk. HflKC, CIII or CSF inhibits the digestion of CII. In wild type E. coli cells, this inhibition is unable to sufficiently stabilize CII, leading to normal plaques (left panel).