EFFECT OF DIHYDROSTREPTOMYCIN ON ESCHERICHIA COLI

Function and origin of mistranslation in distinct cellular contexts

Mistranslation describes errors during protein synthesis that prevent the amino acid sequences specified in the genetic code from being reflected within proteins. For a long time, mistranslation has largely been considered an aberrant cellular process that cells actively avoid at all times. However, recent evidence has demonstrated that cells from all three domains of life not only tolerate certain levels and forms of mistranslation, but actively induce mistranslation under certain circumstances. To this end, dedicated biological mechanisms have recently been found to reduce translational fidelity, which indicates that mistranslation is not exclusively an erroneous process and can even benefit cells in particular cellular contexts. There currently exists a spectrum of mistranslational processes that differ not only in their origins, but also in their molecular and cellular effects. These findings suggest that the optimal degree of translational fidelity largely depends on a specific cellular context. This review aims to conceptualize the basis and functional consequence of the diverse types of mistranslation that have been described so far.

Potential roles for DNA replication and repair functions in cell killing by streptomycin

The aminoglycoside streptomycin binds to ribosomes to promote mistranslation and eventual inhibition of translation. Streptomycin kills bacteria, whereas many other non-aminoglycoside inhibitors of translation do not. Because mistranslation is now known to affect DNA replication, we asked if hydroxyurea, a specific inhibitor of DNA synthesis, affects killing, and find that hydroxyurea significantly attenuates killing by streptomycin. We find that the hydroxyl radical scavengers d-mannitol and thiourea have either no effect or only a modest protective effect. The iron chelator 2,2'-dipyridyl eliminated killing by streptomycin, but further investigation revealed that it blocks streptomycin uptake. Prior treatment of cells with low-levels of methyl methanesulfonate to induce the adaptive response to alkylation leads to a significant attenuation of killing, which, together with the hydroxyurea effect, suggests roles for DNA replication and repair functions in cell killing by streptomycin.

Streptomycinoid Antibiotics: Synergism by Puromycin

Puromycin synergizes the lethal action of streptomycin and related antibiotics. This is interpreted to mean that puromycin action uncovers a sensitive site (or sites) on the 30S ribosome. The streptomycinoid antibiotics can then associate more readily with the ribosome and inhibit further synthesis of valid protein.