Fig. 4. Sensitization of TM9-PhoA to FtsH by addition of extra amino acids to its N-terminus. (A) Amino acid sequences of the predicted N-terminal tail of TM9-PhoA and Z10-TM9-PhoA. The extra sequence in the latter is underlined. (B) Stability of TM9-PhoA and Z10-TM9-PhoA. Each of strains AR5087 (ftsH⁺; lanes 1–4 and 9–12) and AR5090 (ΔftsH; lanes 4–8 and 13–16) was transformed either with pKH472 (TM9-PhoA; lanes 1–8) or pCH43 (Z10-TM9-PhoA; lanes 9–16). The plasmid-bearing cells were grown at 28°C, and induced for lac transcription for 9 min. Cells were pulse-labeled with [³⁵S]methionine for 1.5 min followed by chase with unlabeled methionine for 1, 30, 60 and 120 min. Labeled proteins were immunoprecipitated with anti-PhoA, separated by SDS–PAGE, and visualized. PhoA′ indicates the degradation product.