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Plant Physiology 96:61-68 (1991)
© 1991 American Society of Plant Biologists

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Metabolism and Enzymology

Characterization of Ribonuclease Activity of Three S-Allele-Associated Proteins of Petunia inflata 1

Anuradha Singh, Yunjun Ai and Teh-hui Kao

Department of Molecular and Cell Biology, The Pennsylvania State University, University Park, Pennsylvania 16802

Three S-allele-associated proteins (S-proteins) of Petunia inflata, a species with gametophytic self-incompatibility, were previously found to share sequence similarity with two fungal ribonucleases, RNase T2 and RNase Rh. In this study, the S-proteins from P. inflata plants of S1S2 and S2S3 genotypes were purified to homogeneity by gel filtration and cation-exchange chromatography, and their enzymatic properties were characterized. The three S-proteins (S1, S2, and S3), with pairwise sequence identity ranging from 73.1 to 80.5%, were similar in most of the enzymatic properties characterized. The ribonuclease activity had a pH optimum of 7.0 and a temperature optimum of 50°C. Diethylpyrocarbonate at 1 millimolar almost completely abolished the ribonuclease activity; cupric sulfate and zinc sulfate at 1 millimolar reduced the ribonuclease activity of the three S-proteins by 50 to 75%. EDTA and RNasin had no inhibitory effect. All three S-proteins hydrolyzed polycytidylic acid preferentially, but varied in their nucleolytic activity toward polyadenylic acid and polyuridylic acid.

1 This work was supported by National Science Foundation Grant DCB-8904008, U.S. Department of Agriculture Competitive Grant 90-37261-5560, Inter-College Competitive Grant (Project No. 2997) from the Pennsylvania Agricultural Experiment Station, and Biomedical Research Support Grant from the National Institutes of Health to T.-h. K.




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T.-h. Kao and T. Tsukamoto
The Molecular and Genetic Bases of S-RNase-Based Self-Incompatibility
PLANT CELL, June 1, 2004; 16(suppl_1): S72 - S83.
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Copyright © 1991 by the American Society of Plant Biologists