To test whether a 30S ribosomal subunitformylmethionyl-tRNA-mRNA complex is an obligatory intermediate in protein synthesis, 70S ribosomes from Escherichia coli were crosslinked with the bifunctional imidoester, dimethylsuberimidate. Crosslinked ribosomes contained covelently joined 30S and 50S subunits, as judged by their inability to dissociate at low Mg(2+) concentrations. Treatment of 70S r...

RNase I of Salmonella typhimurium has been purified to a homogeneous state. It has a molecular weight of 2 x 104. Association of RNase I with the 30 S subunits of ribosomes has been investigated by using an inhibition assay. 70 S ribosomes and 30 S subunits, but not the 50 S subunits, inhibit the hydrolysis of polyribonucleotides (only poly adenylic acid was used in the present investigation) b...

Protein synthesis is initiated on ribosomal subunits. However, it is not known how 70S ribosomes are dissociated into small and large subunits. Here we show that 70S ribosomes, as well as the model post-termination complexes, are dissociated into stable subunits by cooperative action of three translation factors: ribosome recycling factor (RRF), elongation factor G (EF-G), and initiation factor...

Ribosomes arranged in pairs (100S) have been related with nutritional stress response and are believed to represent a "hibernation state." Several proteins have been identified that are associated with 100S ribosomes but their spatial organization has hitherto not been characterized. We have used cryoelectron tomography to reveal the three-dimensional configuration of 100S ribosomes isolated fr...

Bottromycin A2 inhibits polylysine synthesis with poly A at low concentrations of E. coli ribosomes. Peptide release by puromycin from ribosomes was significantly inhibited by blasticidin S, chloramphenicol and thiophenicol, but not by bottromycin A2 in the absence of GTPand G factor. Puromycindependent release of peptide from ribosomes was stimulated by the presence of GTP and G factor; it was...

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 subset of mRNAs, polyribosomes, and poly(A)-binding proteins copurify with microtubules from sea urchin embryos. Several lines of evidence indicate that the interaction of microtubules with ribosomes is specific: a distinct stalk-like structure appears to mediate their association; ribosomes bind to microtubules with a constant stoichiometry through several purification cycles; and the presen...

Recent work, reviewed by Gibor and Granickl established that chloroplasts are endowed with their own DNA complement and thus suggested that these organelles with highly specialized functions and an intriguing life cycle are semiautonomous systems, capable of self-replication, and useful as models for the study of differentiation. In addition to their own DNA, chloroplasts were also reported to ...