Accumulation of 70S Monoribosomes in Escherichia coli After Energy Source Shift-Down
AUTOR(ES)
Ruscetti, Francis W.
RESUMO
When Escherichia coli is shifted from glucose-minimal to succinate-minimal medium, a transient inhibition of protein synthesis and a time-dependent redistribution of ribosomes from polysomes to 70S monosomes occurs. These processes are reversed by a shift-up with glucose. In a lysate made from a mixture of log-phase and down-shifted cells, the 70S monosomes are derived solely from the down-shifted cells and are therefore not produced by polysome breakage during preparation. This conclusion is supported by the absence of nascent proteins from the 70S peak. The monosomes are not dissociated by NaCl or by a crude ribosome dissociation factor, so they behave as “complexed” rather than “free” particles. When down-shifted cells are incubated with rifampin to block ribonucleic acid (RNA) synthesis, the 70S monosomes disappear with a half-life of 15 min. When glucose is also added this half-life decreases to 3 min. The 70S particles are stable in the presence of rifampin when chloramphenicol is added to block protein synthesis. We interpret these data to mean that the existence of the 70S monosomes depends on the continued synthesis of messenger RNA and their conversion to free ribosomes (which dissociate under our conditions) is a result of their participation in protein synthesis. Finally, a significant fraction of the RNA labeled during a brief pulse of 3H-uracil is found associated with the 70S peak. These results are consistent with the hypothesis that the 70S monosomes are initiation complexes of single ribosomes and messenger RNA, which do not initiate polypeptide synthesis during a shift-down.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=251250Documentos Relacionados
- Control of Ribosome Synthesis in Escherichia coli: Analysis of an Energy Source Shift-Down
- Control of Protein Synthesis in Escherichia coli: Analysis of an Energy Source Shift-Down
- Effect of Shift-Down and Growth Inhibition on Phospholipid Metabolism of Escherichia coli
- Control of protein synthesis in Escherichia coli: strain differences in control of translational initiation after energy source shift-down.
- Control of protein synthesis in Escherichia coli: control of bacteriophage Q beta coat protein synthesis after energy source shift-down.