Figure 1.

cpSRP is an oligomer containing 54- and 43-kDa subunits. Pea stroma (A and B, solid lines) (5), wheat-germ translated cpSRP54 (C), or cpSRP produced in E. coli (OEcpSRP; A and B, dotted lines) were fractionated by gel filtration and cpSRP54 (A and C) or cpSRP43 (B) were detected by immunoblot analyses (8). The molecular mass of OEcpSRP is larger than that of cpSRP because the former contains cpSRP43 fused to GST. (D) Coimmunoprecipitation of cpSRP43 with antisera against cpSRP54. Coomassie stain of a gel loaded with 2 μg of protein. Stroma was prepared by lysing chloroplasts in 20 mM Hepes-KOH (pH 8.0), 5 mM MgCl₂, 1 mM DTT, and 1 mM phenylmethylsulfonyl fluoride. Samples were fractionated on a Protein Pak 300 SW column in 20 mM of Hepes-KOH (pH 8.0), 5 mM MgCl₂, and 180 mM NaCl at 0.5 ml/min. The column was calibrated using the following proteins as standards: bovine thyroglobulin, 670 kDa; sweet potato β-amylase, 200 kDa; BSA, 66 kDa; ovalbumin, 45 kDa; and cytochrome c, 12 kDa.