Origin of sequence heterogeneity of the small subunit of fraction 1 protein from Nicotiana tabacum.

The partial amino acid sequences of the small subunit of Fraction 1 protein from N. sylvestris, N. tomentosiformis and N. tabacum were determined. The sequence of N. sylvestris is NH2. Gln-Val-Trp-Pro-Pro-Ile-Asn-----Tyr COOH. In the sequence up to the 7th amino acid and C-terminus, differences were only found at the 6th position in the three species, where N. sylvestris and N. tomentosiformis show Ile and Tyr, respectively. N. tabacum show both Ile and Tyr in almost equal amount at this position. These results confirmed a previous hypothesis that N. tabacum had been evolved through the hybridization of N. sylvestris and N. tomentosiformis.