Ribosomal proteins S5, S11, S13 and S19 localized by ekectron microscopy of antibody-labeled subunits

Abstract

Specific antibodies prepared against purified Escherichia coli small subunit proteins were used to map protein locations by electron microscopy of bound antibody in negatively contrasted small subunit preparations. By identifying and interpreting characteristic views as projections of a single structure, the protein distributions on the surface of the small subunit have been mapped in three dimensions. Antibodies against ribosomal proteins S5, S11 and S13 bind to single regions of the ribosome surface. In contrast, anti-S19 immunoglobulin G binds to two separated regions of the ribosome surface, suggesting that S19 has an elongated conformation in situ. Proteins S13 and S19 are located on the smaller portion of elongated profiles, while S5 and S11 are located on the larger portion of the subunit profile, near the partition traversing the subunit image. The locations of exposed regions of S11, S13 and S19, in combination with the crosslinking results of others, suggest a binding site for initiation factor IF3 on a region of the 30 S surface, comprising the platform, the cleft, part of the partition, and part of the upper “one third” of the subunit.