Nucleic Acids Research, 1978, Vol. 5, No. 8 2789-2800
© 1978
Articles |
On the role of protein S4 N-terminal residues I through 30 in 30S ribosome function
Laboratory of Molecular Biology and Department of Genetics, University of Wisconsin Madison, WI 53706, USA
Received May 22, 1978. 30S ribosomal protein S4 contains a single cysteine residue at position 31. We have selectively cleaved the peptide bond adjacent to this residue using the reagent 2-nitro-5-thiocyano-benzoic acid. The two resultant fragments were purified. The smaller S4-fragment (1–30) was found to be incapable of interacting with 16S RNA directly. This fragment also is not incorporated into a particle reconstituted from 16S RNA and 20 purified proteins with S4 missing. In contrast, the large S4- fragment (31–203) appears to be fully functional in ribosome assembly. Replacement of S4 with this fragment in the reconstitution reaction leads to a complete 30S ribosome containing all 30S proteins. This particle has a full capacity to bind poly U but has lost all activity for poiy U directed phe-tRNA binding. We therefore propose that the N-terminus of protein S4 is not critical for ribosome assembly but is essential for tRNA binding.