Nuclear Gene-Regulated Expression of Chloroplast Genes for Coupling Factor One in Maize

In order to gain a better understanding of the interaction between the chloroplast and nuclear genomes in controlling the expression of plastid genes and the biosynthesis of chloroplast proteins, maize (Zea mays) nuclear gene mutant hcf(*)-38, in which alpha and beta subunits of coupling factor one (CF(1)) are almost completely missing was studied. The mutant possesses all the other subunits of CF(1) but several peptides of photosystem II are present in reduced amounts. A competitive hybridization experiment showed the presence of the same plastid mRNA species in mutant and wild-type plants except for slightly lower levels of some transcripts in the mutant. Northern hybridization and dot blot hybridization experiments showed the features of transcripts for alpha and beta subunits of CF(1) in the mutant to be similar to those in the wild-type maize although their levels are somewhat lower in the mutant. In vivo and in organello protein labeling experiments with L-[(35)S]Met have shown that alpha and beta subunits of CF(1) are synthesized, assembled into CF(1), and probably associated with thylakoid membranes in mutant plants. It is concluded that they are subsequently degraded.