Evolutionary conservation of chloroplast genes coding for the large subunits of fraction 1 protein.

Crystalline fraction 1 protein, obtained from four species of Nicotiana, have identical polypeptide compositions and isoelectric points. However, the tryptic peptide map of the large subunit of this protein from N. knightiana and N. paniculata differs from that of N. tomentosa and N. tomentosiformis. Since the large subunits of fraction 1 protein are coded by chloroplast DNA, the difference in their primary structure reflects the structural changes of the chloroplast genes containing the coding information. This indicates that the rate of mutation of chloroplast DNA seems to be higher than predicated from the analysis of isoelectric points of this protein.