Ready M P, Katzin B J, Robertus J D
Clayton Foundation Biochemical Institute, Department of Chemistry, University of Texas, Austin 78712.
Proteins. 1988;3(1):53-9. doi: 10.1002/prot.340030105.
Plant ribosome-inhibiting proteins are shown to be homologous at the domain level to RNase H from Escherichia coli and to two regions of the pol gene product of retroviral reverse transcriptases. One of these regions carries the viral integrase or int function, while the other has previously been suggested to contain the viral RNase H exo activity. Several residues conserved among the ribosome inhibitors, E. coli RNase H, and the integrase proteins are seen to occupy a prominent cleft in the tertiary structure of the ribosome inhibitor ricin, suggesting roles in binding or catalysis. It is likely that these homologous sequences represent modern derivatives of an ancient protein-folding unit capable of nucleic acid binding and modification which has been incorporated into a variety of enzyme functions.
植物核糖体抑制蛋白在结构域水平上与大肠杆菌的核糖核酸酶H以及逆转录病毒逆转录酶的pol基因产物的两个区域同源。其中一个区域具有病毒整合酶或int功能，而另一个区域先前被认为含有病毒核糖核酸酶H的外切酶活性。核糖体抑制剂、大肠杆菌核糖核酸酶H和整合酶蛋白之间保守的几个残基在核糖体抑制剂蓖麻毒素的三级结构中占据一个突出的裂缝，表明它们在结合或催化中起作用。这些同源序列很可能代表了一个古老的能够进行核酸结合和修饰的蛋白质折叠单元的现代衍生物，该单元已被纳入多种酶功能中。
