Figure 8.

Nitrogen Stress-Induced Phosphorylation of the Ser-49 Residue of the P_II Protein in the Wild Type and FtsH1down Mutant.

The tryptic peptides GSEYTVEFLQK and YRGSEYTVEFLQK (representing a missed cleavage site) from P_II (Ssl0707), with the Ser-49 residue shown in bold, were detected by MS and database searching, as described in Methods. YRGSEYTVEFLQK was also identified as phosphorylated at Ser-49, as confirmed by product ion spectra shown in Supplemental Figure 6. Occupancy ratios are expressed as YRGpSEYTVEFLQK ion intensity (phos)/(GSEYTVEFLQK + YRGSEYTVEFLQK + YRGpSEYTVEFLQK) ion intensities. The phosphopeptide was only detected in two of the analyses in the FtsH1down mutant under nitrogen sufficiency; therefore, the mean ratio ± sd is n = 2. All other analyses were n = 9 (3× biological and 3× technical replicates).