TOPOGRAPHY OF RIBOSOMAL-PROTEINS - REVISED PROTEIN MAP OF THE SMALL RIBOSOMAL-SUBUNIT

Exposure of proteins on the surface of the small (30S) ribosomal subun it of Escherichia coli was studied by the hot tritium bombardment tech nique (tritium planigraphy). Eight of 21 proteins of the 30S subunit ( S3, S8, S10, S12, S15, S16, S17, and S19) had virtually no groups expo sed on the surface of the particle, i.e., they were mainly hidden insi de. Seven proteins (S1, S4, S5, S7, S18, S20, and S21) were well expos ed on the surface of the particle, thus being outside proteins. The re maining proteins (S2, S6, S9, and/or S11, S13, and S14) were partially exposed. On the basis of these results, a revised three-dimensional p rotein map of the small ribosomal subunit is presented and a corrected model is proposed.