Initiation of protein synthesis in isolated mitochondria and chloroplasts

Abstract

N 5-Formyltetrahydrofolate, a competitive inhibitor of the formylation of the initiator Met-tRNA fMet in an in vitro assay, is a powerful inhibitor of amino acid incorporation in isolated Saccharomyces cerevisiae mitochondria and in Euglena gracilis chloroplasts. Thus, a large part of the incorporation is dependent upon new initiation acts. On the contrary, the rate of incorporation can be largely increased by addition of the specific formyl group donor, N 10-formyltetrahydrofolate. Experiments are also reported strongly suggesting that the formylation of Met-tRNA fMet is an absolute requirement in order to initiate protein synthesis in chloroplasts, as has been shown in mitochondria.