Change in the solubility of crystalline Fraction I proteins correlated with change in the composition of the small subunit

摘要

Fraction I protein crystals were obtained by a simple method from four additional species in addition to seven species ofNicotianapreviously reported and fromSolanum melongena. Crystals were obtained neither from several other genera of the Solanaceal nor fromN. debneyi, but14C protein from the latter co-crystallized withN. tabacumFraction I protein. Co-crystallization did not occur with14C proteins from species ofTagetes, Allium, Beta, BrassicaandHyocyamuswhose Fraction I proteins were evidently too different in their quaternary structures to occupy the same crystal lattice withN. tabacumprotein. Fraction I proteins fromN. gosseiandN. excelsiordiffered in solubility as a function of the NaCl concentration. The two proteins were alike in the isoelectric point of the three primary peptides composing the large subunit, but differed in the isoelectric point of one out of four primary peptides of the small subunit; this difference was also consistent with a difference in tryptic peptide fingerprints. Proteins fromN. tabacumandN. glaucadiffered both in the composition of their large and small subunits but did not differ in solubility. However, by changing the composition of the small subunit without changing the large subunit, the solubility of each protein was changed. The change in small subunit composition could be achieved by isolating proteins from the reciprocal F1hybrids ofN. tabacum×N. glaucawhere the maternal inheritance regulates the composition of the large subunit, whereas both maternal and paternal genes regulate the composition of the small subunit