An in vitro protein-synthesizing system with isolated chloroplasts of Sorghum vulgare. An alternate assay system for exogenous template RNA.

A light-dependent in vitro protein-synthesizing system from isolated mesophyll chloroplasts of Sorghum vulgare was characterized. Preincubation of chloroplasts in light at 25 degrees C for 1 h depleted the endogenous templates completely; such preincubated chloroplasts translated exogenously added homologous, heterologous, and synthetic templates efficiently. The fidelity of the system in translating added templates was tested with specific templates. Substantive evidence for the fidelity of the system was obtained by immunological analysis of the specific products, e.g. chloroplast coupling Factor I obtained by the translation of S. vulgare leaf cellular and chloroplast RNAs. The efficiency of the system in translating the exogenous mRNA was also quite high. As the endogenous mRNA was totally depleted during preincubation, and as the system was nonspecific for the source of RNA for translation, these chloroplasts can serve as a simple alternative system for assaying the role of diverse template RNAs.