Imported cpTatC Faithfully Integrates into Thylakoids in Amounts Greater Than Endogenous cpTatC.
(A) Radiolabeled precpTatC (lanes 1 to 4), precpTatC-His (lanes 5 to 8), and precpTatCaaa (lanes 9 to 12) were incubated with isolated chloroplasts in protein import assays. The chloroplasts were then fractionated to stroma (S) and membranes (M). Membranes were treated with thermolysin (+T). Lanes labeled “tp” contain in vitro–translated cpTatC precursors used. Samples were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. DP, thermolysin degradation product.
(B) The abundance of imported cpTatC is comparable to endogenous cpTatC. cpTatC precursors (tp) and the membrane samples recovered from mock import and precpTatC import assays (M) were analyzed by immunoblotting with α-cpTatC antibody. Mock import underwent all assay procedures but received no precursor protein.