Chloroplast DNA codes for the ribulose diphosphate carboxylase catalytic site on fraction I proteins of Nicotiana species

Summary

The specific activity of ribulose diphosphate carboxylase and the K _m for ribulose 1–5 diphosphate of Fraction I protein isolated from N. gossei was significantly higher than enzyme from six other species of Nicotiana which were closely similar to each other. In several interspecific, reciprocal F₁ hybrids, the higher N. gossei activity was present only when N. gossei was the female parent. Consequently, the maternal mode of inheritance indicates chloroplast DNA to contain information which regulates the conformation of the catalytic site on the enzyme. Previous results had shown this DNA to code for the primary structure of the large subunit. In hybrids where N. gossei was the female parent, the specific enzyme activity was intermediate between N. gossei itself and the other parent because of formation of isozymes of Fraction I protein which were demonstrated by tryptic peptide fingerprints of the small subunits of Fraction I protein from N. gossei, N. excelsior, and reciprocal hybrids. Peptides characteristic of the enzyme from each parent were found in both hybrids. Previous results had demonstrated that nuclear genes contain the code for the small subunit. In the hybrid where N. gossei is the female parent, the reduction in specific enzyme activity from that of N. gossei itself is evidently the result of N. excelsior type small subunits modifying the catalytic site on the N. gossei type of large subunits. A “hybrid” protein of lesser activity is produced which dilutes the higher activity of the N. gossei type protein.