A system capable of incorporating amino acids into protein has been prepared from chloroplasts isolated from spinach leaves. The activity of the system is inhibited by chloramphenicol or RNase but not by rifampycin or cycloheximide. After reducing the endogenous activity by treatment with micrococcal nuclease, the system responds to homologous or heterologous mRNAs. The RNA from MS-2 phage is translated faithfully as demonstrated by the isolation from the translation products of a protein with the same mobility of the phage coat protein. Partial proteolytic digestion confirmed that the protein synthesized in vitro is indeed the phage protein.
