Functional domains of Escherichia coli ribosomal protein S1 : Formation and characterization of a fragment with ribosome-binding properties

Abstract

Treatment of Escherichia coli ribosomal protein S1 with TPCK-treated trypsin under mild conditions (0 °C, 1 to 2 μig trypsin/mg S1 protein) results in the production of a high molecular weight fragment in yields of up to 80% within a few minutes. The fragment is relatively resistant to further degradation. We have isolated the fragment in pure form for structural and functional characterization. The fragment (denoted S1-F1) has a molecular weight of 48,500 as shown by sodium dodecyl sulphate gel electrophoresis, and therefore it contains approximately 60% of the amino acid residues of S1. The N-terminal sequence of the fragment is different from that of intact S1. The fragment binds to the 30 S ribosomal subunit and to polyuridylic acid in approximately the same manner as intact S1, indicating that the active centres of S1 concerned with these two characteristic binding properties are localized within the fragment. In spite of the above properties, the fragment was completely unable to support protein synthesis. The significance of these results in relation to the structure and function of S1 is discussed.