## 2 Results  
### Components of the Transcriptional Apparatus  
Figure 1 indicates that the abundance pattern of the 39 proteins of the transcriptional apparatus is utterly different between \(SL\) and \(SC\) and fall into four major clusters (a to d). Proteins of cluster a were more abundant in Pi limitation than in Pi proficiency in \(SC\) as well as in \(SL\) to a lesser extent; proteins of cluster b were more abundant in \(SC\) than in \(SL\) in  
both Pi conditions, whereas it was the opposite for proteins of cluster c, and proteins of cluster d were more abundant in Pi proficiency than in Pi limitation in both strains. Cluster a includes 12 proteins rather more abundant in \(SC\) than in \(SL\) in Pi limitation especially at 60 h. This cluster includes the principal sigma factor HrdB/SCO5820 [15; 16; 17], two subunits of the core RNA polymerase, RpoA/SCO4729 [18] and RpoC/SCO4655 [19]; the sigma factors SCO3613 and SigR that is a major regulator positively controling the expression of numerous genes involved in resistance to oxidative stress (OxS) [20; 21; 22; 23; 24], the anti-sigma factor SCO5244 and the anti-sigma factor antagonist BldG [25] are involved in the regulation of the activity of the osmotic stress (OsS) responsive sigma factor H [26; 27], as well as the RNA polymerase-binding protein Dksa-like SCO6164. Proteins of this family are thought to stabilize ppGpp binding to RNA polymerase [28; 29] but the function of SCO6164 is still unclear in Streptomyces. Four proteins of cluster A were also abundant in \(SL\) in Pi proficiency at both time points. It includes the ECF sigma factor BldN/SCO3323 required for aerial mycelium formation [30; 31]; RpoZ/SCO1478 [32] that was shown to play a positive role in the regulation of morphological differentiation and antibiotic production [33]; the anti-termination protein NusG/SCO4647 [34], and the RNA nucleotidyltransferase SCO3896 [35]. Cluster b includes 16 proteins more abundant in \(SC\) than in \(SL\) in both Pi conditions. This cluster includes the \(\beta\) subunit RpoB/SCO4654 of the core RNA polymerase able to  
Figure 1: Heatmap representation of the abundance of components of the transcriptional apparatus of \(SL\) and SC that can be divided in 4 sub-clusters a, b, c and d. Cluster a includes 12 proteins rather more abundant in \(SC\) than in \(SL\) in Pi limitation especially at 60 h. Cluster b includes 16 proteins more abundant in \(SC\) than in \(SL\) in both Pi conditions. Cluster c includes 7 proteins more abundant in \(SC\) than in \(SC\) in both Pi conditions. Cluster d includes 4 proteins more abundant in Pi limitation in both Pi conditions. Cluster d includes 4 proteins more abundant in Pi limitation in both strains but mainly at 60 h.  
interact with the stringent factor ppGpp [36], the RNA binding protein RbpA/SCO1421 that promotes the binding of the vegetative sigma factor to the core RNA polymerase [37], the transcription termination factor Rho/SCO5357 [38], and the transcription elongation factor SCO5704/NusA. The principal sigma factor HrdD/SCO3202 might be involved in the response to various stresses [39] and SigH/SCO5243 is involved in the response to OsS. It directs the transcription of the gene encoding the ECF sigma factor SigJ [40] and plays a positive role in the regulation of morphological differentiation and ACT production [41; 42; 43]. Cluster b also includes seven ECF-like sigma factors [44; 45] such as SigE/SCO3356 and SigU/SCO2954, as well as SCC00803, SCO0866, SCO3626, SCO4409, and SCO4895. SigE belongs to a signal transduction system sensing and responding to general cell wall stress and is required for normal cell wall structure [46; 47]. SigE contributes to the regulation of HrdD expression [48] and plays a negative role in the regulation of ACT biosynthesis [47; 49]. SigU positively controls the expression of numerous genes encoding secreted proteins including proteases that may be important to combat cell wall stress [50] and it has a negative impact on morphological differentiation [51].