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As reported in previous papers (Moon et al., 1987a, b), one Labelle fine of rice (03= sativum) has two different chloroplast DNA fragments (Ct-I and Ct-3) which contain a gene cluster, rbcLratpp-atpe-trnM-trnV. It was revealed that the majority of the ct genomes contain Ct-3 fragment, while Ct-1 is contained in less than 1/10 of ct genomes. Detailed sequencing analysis also revealed that all the above five genes contained in Ct-3 (major population) are functional, whereas in Ct-1 (minor population), the rbcL is truncated, and atpo has a single base-pair substitution in the 5´-noncoding and four single base-pair deletions in the coding region. Existence of mutations in these essential genes raises questions about the proper expression and the function of the gene. To discuss this point, in this communication, I present data from chloramphenicol acetyl transferase (CAT) assay and Western blot analysis of the mutated atpp gene in the minor population. The results revealed that the expression level of the gene is considerably low due to the low copy number and the promoter mutation. The data from Northern blot analysis strongly suggest that the mutant protein can not be assembled to form a functional ATP synthetase complex, and they are rapidly degraded whithout being accumulated. This is presumably due to the mutations in the coding region which can cause gross defectiveness in protein products. In conclusion, the existence of mutant atpo gene as the minor population does not interfere with the function of the ATP synthetase.
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