Protein synthesis in chloroplasts I. Light-driven synthesis of the large subunit of Fraction I protein by isolated pea chloroplasts

Abstract

Intact isolated pea chloroplasts use light energy to incorporate labelled amino acids into protein. 25 % of this incorporation is present in a 150 000 × g chloroplast supernatant fraction. When this supernatant is analysed on sodium dodecyl sulphate polyacrylamide gels only one polypeptide is labelled. This polypeptide is the large subunit of Fraction I protein, a major protein constituent of the chloroplast. Identity of the soluble in vitro product with the large subunit of Fraction I protein was established by comparing a tryptic map of its [ 35S]methionine-labelled peptides with a tryptic map of the large subunit of Fraction I protein labelled in vivo with [ 35S]methionine. We conclude that only one of the many chloroplast soluble proteins, namely the large subunit of Fraction I protein, is synthesised on chloroplast ribosomes.