IDENTIFICATION AND PARTIAL AMINO-ACID-SEQUENCES OF 7 S-RNASES ASSOCIATED WITH SELF-INCOMPATIBILITY OF JAPANESE PEAR, PYRUS-PYRIFOLIA NAKAI

S-allele-specific proteins (S-proteins) were separated and identified by two-dimensional (2D) gel electrophoresis from the style extract of 14 cultivars of Japanese pear, Pyrus pyrifolia Nakai, which exhibits g ametophytic self-incompatibility. These S-proteins were 30-32 kDa basi c proteins with putative pIs of 9.6-10.1 and were distinct from the ot her proteins, which were common for all cultivars examined. Each S-pro tein was assigned 60 a given S-genotype based on electrophoretic mobil ity and the partial amino acid sequence. For S-1- to S-7-proteins, fiv e different N-terminal amino acid sequences sharing the YFQFTQQY seque nce were determined. Since the same N-terminal amino acid sequences we re found for both S-1- and S-7-proteins, and for S-3- and S-5-proteins , the two S-proteins of each pair were distinguished based on their el ectrophoretic behavior, The internal amino acid sequences of S-2- and S-4-proteins, determined for Achromobacter protease I (API) digests, r evealed that these proteins are S-2- and S-4-RNases, respectively. In the cultivar Nijisseiki, these two RNases were expressed from the whit e bud to mature flower stages when the cultivar acquires and enforces self-incompatibility. Osa-Nijisseiki, a self-compatible mutant of Niji sseiki, produced S-2-RNase, but did not produce S-4-RNase, The absence of S-4-RNase was also observed in self-compatible offsprings derived from Osa-Nijisseiki, These results suggest that Japanese pear in the f amily Rosaceae possesses a gametophytic self-incompatibility system in volving an S-RNase, and that a reduction or lack of expression of S-4- RNase in the style is responsible for the self-compatibility of Osa-Ni jisseiki.