Singh A, Ai Y, Kao T H
Department of Molecular and Cell Biology, The Pennsylvania State University, University Park, Pennsylvania 16802.
Plant Physiol. 1991 May;96(1):61-8. doi: 10.1104/pp.96.1.61.
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 T(2) and RNase Rh. In this study, the S-proteins from P. inflata plants of S(1)S(2) and S(2)S(3) genotypes were purified to homogeneity by gel filtration and cation-exchange chromatography, and their enzymatic properties were characterized. The three S-proteins (S(1), S(2), and S(3)), 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 degrees 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.
矮牵牛是一种具有配子体自交不亲和性的物种，先前已发现其三种S等位基因相关蛋白（S蛋白）与两种真菌核糖核酸酶RNase T(2)和RNase Rh具有序列相似性。在本研究中，通过凝胶过滤和阳离子交换色谱法将S(1)S(2)和S(2)S(3)基因型的矮牵牛植株中的S蛋白纯化至同质，并对其酶学性质进行了表征。三种S蛋白（S(1)、S(2)和S(3)）的两两序列同一性在73.1%至80.5%之间，在所表征的大多数酶学性质方面相似。核糖核酸酶活性的最适pH为7.0，最适温度为50℃。1毫摩尔的焦碳酸二乙酯几乎完全消除了核糖核酸酶活性；1毫摩尔的硫酸铜和硫酸锌使三种S蛋白的核糖核酸酶活性降低了50%至75%。EDTA和核糖核酸酶抑制剂没有抑制作用。所有三种S蛋白均优先水解聚胞苷酸，但对聚腺苷酸和聚尿苷酸的核酸分解活性有所不同。
