Synthesis of the alpha and beta subunits of coupling factor 1 by polysomes from pea chloroplasts

Washed thylakoids of pea chloroplasts, containing tightly bound polysomes, incorporate radioactive amino acids into protein when supplied with soluble factors from Escherichia coli. Polyacrylamide gel electrophoresis with lithium dodecyl sulfate, followed by autoradiography of the labeled products, showed the synthesis of a number of different polypeptides. Two of the most heavily labeled products were in the region expected for the alpha and beta subunits of coupling factor 1, at 57 and 54 kDa. Positive identification of the subunits was made using monospecific antibodies. Furthermore, the same two polypeptides made by soluble polysomes located in the chloroplast stroma were found. While the major proportion of the newly formed alpha and beta subunits made by thylakoid-bound polysomes remained with the thylakoids after protein synthesis occurred, no evidence was found of incorporation into complete, EDTA-extractable coupling factor 1.