PLACEMENT OF DINITROPHENYL-MODIFIED RIBOSOMAL-PROTEINS IN TOTALLY RECONSTITUTED ESCHERICHIA-COLI 30-S SUBUNITS - LOCALIZATION OF PROTEIN-S6, PROTEIN-S13, PROTEIN-S16, AND PROTEIN-S18 BY IMMUNE ELECTRON-MICROSCOPY

Purified Escherichia coli ribosomal proteins S6, S13, S16, and S18 wer e dinitrophenylated at their amino termini and/or at one or more inter nal lysine residues. Each dinitrophenyl protein was then separately in corporated into reconstituted small ribosomal subunits. Modified prote ins were localized on the 30 S subunit surface by electron microscopy of reconstituted subunits complexed with antibodies to dinitrophenol ( DNP). DNP protein S13 was placed on the subunit head above the platfor m and on the surface that faces the large subunit. DNP-S18 was localiz ed to the subunit platform below the tip and in a region associated wi th binding to 50 S subunits. DNP proteins S6 and S16 were both localiz ed near the junction of the subunit body and platform; DNP-S6 was avai lable to antibody in 70 S ribosomes and was placed on the cytoplasm-fa cing side of the subunit in an area that overlaps the platform and bod y of the particle. DNP-S16 in 70 S ribosomes was not bound by antibody . It was localized to the 30 S body near its junction with the platfor m and on the surface facing the 50 S particle. The results complement and clarify data obtained using other approaches.