The effect of rifampin, an inhibitor of bacterial DNA-dependent RNA polymerase, was studied in Chlamydomonas reinhardi. It was shown, in vivo and in vitro, that chloroplast-located, but not nuclear, DNA-dependent RNA polymerase is inhibited by this drug. The inhibition of chloroplast RNA polymerase results in the inhibition of chloroplast rRNA synthesis, and thus in the loss of chloroplast ribosomes. The ability to carry out photosynthesis is also lost after prolonged heterotrophic growth in the presence of rifampin, but cell division and chloroplast replication are not affected. It is proposed that chloroplast DNA contains information for chloroplast rRNA, but this DNA does not have the information for chloroplast DNA polymerase. Moreover, the DNA polymerase is not synthesized on chloroplast ribosomes
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