Nascent peptide as sole attachment of polysomes to membranes in bacteria.

When membrane-polysome complexes from Escherichia coli were treated with puromycin, at various Mg2+ and K+ concentrations, the bulk of the ribosomes were released from the membrane. Moreover, many released ribosomes released ribosomes remained attached to mRNA (pseudopolysomes). These results suggest that ribosomes are attached to the membrane in bacteria solely by their nascent chain. Without a direct attachment the conformational changes associated with chain elongation on the ribosome cannot force the growing chain through the membrane, and so alternative sources of energy for the transfer must be considered.