## 3 Results
### CII Complementation
In the _rpoB_ mutant BI (Table 3), CII expression from plasmids [cII] and [cII\({}_{1-92}\)] (but not [cII\({}_{1-87}\)]) yielded high level complementation, blocking lytic phage growth at 39 \({}^{\circ}\)C. The remaining _rpoB_ mutants (B8, C1, C4, C10, D2, D6) interfered with CII complementation, Table 3. This result supports the conclusion that a CII-RpoB interaction participates in CII complementation. The loss of any CII complementation by [cII\({}_{1-87}\)] in five of seven _rpoB_ mutants suggests that an interaction between the terminal ten amino acids of CII and RpoB is an essential component of CII-stimulated \(pE\) transcription. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Host [Plasmid] 1  & \multicolumn{1}{c}{**39 \({}^{\circ}\)C**} \\ \hline
594 [cII] = [cII\({}_{1-87}\)] & H (high) & – & 0.03 (0.001) [0] & \textless{}0.001 (0.0001) [100] \\
594 [cII-opo-PO94] & 0 (none) & + 4 & 0.59 (0.03) [0] & 0.08 (0.03) [0] \\
594 [cII\({}_{1-87}\)] & H & – & 0.73 (0.01) [0] & 0.05 (0.001) [100] \\
594 [cII\({}_{1-87}\)] & H & – & 0.76 (0.02) [0] & 0.08 (0.03) [0] \\
594 [cII\({}_{1-77}\)] & 0 & + 4 & 0.74 (0.10) [0] & 0.32 (0.10) [0] \\
594 [cII\({}_{1-63638}\)[38,642 A-G, M-V]) & H & – & 0.62 (0.10) [0] & 0.002 (0.0008) [89] \\
594 [cII\({}_{1-63638}\)[38,634 A-G, Q-R] & H & – & 0.76 (0.02) [0] & \textless{}0.001 (-0.001) [19] \\
594 [cII\({}_{1-3638}\)[3638]] & H & – & 0.65 (0.04) [0] & \textless{}0.001 (-0.001) [6] \\
594 _hftA_::kan [cII\({}_{1-87}\)] & S (slight) & + & 0.89 (0.01) [0] & 0.008 (<0.001) [100] \\
594 _hftA_::kan [cII\({}_{1-2}\)] & S & + & 0.69 (0.01) [0] & \textless{}0.001 (-0.001) [100] \\
594 _hftA_::kan [cII\({}_{1-87}\)] & S & + & 0.58 (0.02) [0] & 0.24 (<0.001) [0] \\
594 _hftA_::kan [cII\({}_{1-77}\)] & 0 & + 4 & 0.86 (0.10) [0] & 0.58 (0.01) [0] \\
594 _hftA_::kan [cII\({}_{1-92}\)] & 0 & + 4 & 0.63 (<0.001) [0] & 0.001 (0.002) [100] \\
594 _hftA_::kan [cII\({}_{1-87}\)] & 0 & + 4 & 0.001 (0.01) [67] & \textless{}0.001 (0.003) [100] \\
594 _ppnB_::kan [cII\({}_{1-60}\)-porP094] & 0 & + 4 & 0.046 (0.01) [64] & \textless{}0.001 (0.0003) [89] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Influence of C-terminal _cl1_ amino acids and host properties on _cl1_ complementation, toxicity and plasmid loss. Figure 3: CII _trans_-complementation assay. Top shows complementation results (additional examples are shown in Figures S2 and S3). The cartoon shows the sequential steps, A to D required for CII complementation. Each step is indicated by either dotted (steps A and D) or solid (steps B and C) lines. Steps: A _cII_ expression occurs from plasmid pclpR-cII-timm in 594 cells upon shifting cells grown at 30 \({}^{\circ}\)C to 37–42 \({}^{\circ}\)C. This inactivates the CI\({}_{\lambda}\) repressor, enabling transcription from plasmid promoter _pR_ through gene _cII_. B CII protein encoded by plasmid stimulates repressor-establishment transcription from promoter _pE_ on phage genome after 594 [pclpE-cII-timm] cells are infected with phage \(\lambda\)_imm_434_cII_2002. C High expression of the CI\({}_{434}\) repressor protein occurs from CII-stimulated _pE_-mRNA transcribed from infecting phage genome. D CI\({}_{434}\) repressor binds the _o_L\({}_{434}\) and _o_R\({}_{434}\) operator sites preventing leftward and rightward transcription and blocking lytic phage growth. The potential for OOP RNA expression from plasmid pclpR-cII-oop-pO nullifies CII-activation of _pE_-dependent CI\({}_{434}\) expression at 37–39 \({}^{\circ}\)C. The results for infections with \(\lambda\)_imm_434_cII_68 were identical to infections with \(\lambda\)_imm_434_cII_2002.