To elucidate the function of S-allele and the possible molecular mechanism of gametophytic self-incompatibility (GSI) in Chinese white pear (Pyrus bretschneideri Rehd.), full length cDNA encoding S
20
-RNase was cloned by rapid amplification of cDNA ends (RACE) approach from the cultivar 'Donghuang' (S
8
S
20
), and analyzed by bioinformatics method. S
20
-RNase displayed typical sequence features of pear S
20
-RNases, i.e. five conserved regions and a hypervariable (HV) region. The predicted three-dimension (3D) structure of the S
20
-RNase was similar to that of 53-RNase of Japanese pear (P....