Figure 5.

Biosynthesis and degradation of the D1 protein. A, Biosynthesis of the D1 protein under HL conditions. The pgsA mutant cells grown under LL conditions for 5 d in the presence (+PG) or absence (–PG) of PG were transferred to HL conditions for 120 min. Cells were pulse labeled with [³⁵S]Met for 10 min at the beginning (lane 1) or at the end (lane 2) of HL treatment. B, Degradation of the D1 protein under HL conditions. The pgsA mutant cells grown under LL conditions for 5 d in the presence (+PG) or absence of PG (–PG) were labeled with [³⁵S]Met under LL conditions for 30 min, and thereafter radioactivity was chased for 0 (lane 1), 30 (lane 2), 60 (lane 3), or 120 min (lane 4) under HL conditions in the presence of nonradioactive Met. C, Degradation of the D1 protein under LL conditions after HL treatment. The pgsA mutant cells grown under LL conditions for 5 d in the absence of PG were preincubated for 100 min under HL conditions and then labeled with [³⁵S]Met for 20 min under HL conditions. Thereafter, these cells were transferred to LL conditions in the presence (+PG) or absence (–PG) of PG, and the radioactivity was chased for 0 (lane 1), 15 (lane 2), or 60 min (lane 3) in the presence of nonradioactive Met. The top panel in each figure depicts an autoradiogram showing the incorporation of radioactive Met into the D1 protein, and the bottom panel shows the steady state of the D1 protein detected by western-blot analysis with the same membranes.