Sulfhydryl groups of Escherichia coli ribosomal protein S1. Location along the polypeptide chain

The location of the functionally important -SH groups of Escherichia coli ribosomal protein S1 along the polypeptide chain has been determined using a cysteine-specific cleavage procedure. The two -SH groups of S1 are located at 57% and 67% of the polypeptide chain length from the NH2 terminus. The -SH group farther from the NH2 terminus is shown to be the more reactive one. Two truncated derivatives of S1 (S1-F1 and m1-S1) both contain two -SH groups. It has previously been shown that S1-F1 (which lacks the NH2-terminal region of S1) is inactive in unfolding nucleic acids, just as the N-ethylmaleimide derivative of S1. The present results therefore show that the formation and functioning of the nucleic acid unfolding domain of protein S1 requires the -SH group(s) as well as the NH2-terminal region.