Key result
The mutant m1-S1 retained nucleic acid binding and unwinding abilities similar to wild-type S1, whereas the S1-F1 fragment bound to some nucleic acids but lost all unwinding ability.
The ability of ribosomal protein S1 to unwind RNA correlates with its function in protein synthesis.
Unwinding activity of S1, separable from binding, correlates with translation function; hypothesis-generating for ribosomal mechanisms.
The nucleic acid binding and unwinding properties of wild-type Escherichia coli ribosomal protein S1 have been compared to those of a mutant form and a large trypsin-resistant fragment, both reported recently [J. Mol. Biol. 127, 41-45 (1979) and J. Biol. Chem. 254, 4309-4312 (1979). The mutant (m1-S1) contains 77% and the fragment (S1-F1) 66% of the polypeptide chain length (approximately 600 amino acid residues) of protein S1. The mutant is active in protein synthesis in vitro; the fragment, although retaining one or more of the functional domains of S1, is inactive in protein synthesis. We find that m1-S1 is is almost as effective as S1 in binding to poly(rU), phage MS2 RNA and simian virus 40 (SV40) DNA, and in unfolding poly(rU) and the helical structures present in MS2 RNA and phi X174 viral DNA. S1-F1, however, binds to poly(rU) and denatured SV40 DNA, but not to MS2 RNA. It unfolds neither poly(rU), nor the residual secondary structure of MS2 RNA or phi X174 viral DNA. Thus, there appears to be a correlation between the loss in ability of S1 to unwind RNA and the loss in its ability to function in protein synthesis.
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Thomas et al. (1979) studied this question. Mutant m1-S1 and fragment S1-F1 of ribosomal protein S1 vs. Wild-type Escherichia coli ribosomal protein S1 was evaluated on Nucleic acid binding and unwinding properties. The mutant m1-S1 retained nucleic acid binding and unwinding abilities similar to wild-type S1, whereas the S1-F1 fragment bound to some nucleic acids but lost all unwinding ability.
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