Physiological and genetic responses of bacteria to osmotic stress.

https://mmbr.asm.org/content/mmbr/60/1/44.full.pdf

Histidine biosynthetic pathway and genes: structure, regulation, and evolution.

A class of mutations that increase the deficiency of a suppressor tRNA in translating a particular amber codon has been characterized. The increased efficiency is due to a mutation resulting in a change in the mRNA that affects the nucleotide adjacent to the 3' side of the UAG triplet. Thus the interaction of tRNA with mRNA is influenced by mRNA sequences outside the triplet codon.

The influence of codon context on genetic code translation

Context effects: Translation of UAG codon by suppressor tRNA is affected by the sequence following UAG in the message

Publisher Summary This chapter discusses that the suppressor mutations are one class of secondary mutations that modify the phenotype in the presence of the originally mutant gene. In contrast to “enhancers” that make the mutant phenotype more extreme, suppressor mutations yield organisms phenotypically more like the wild type: The mutant phenotype is “suppressed.” Thus, suppressors are mutations that elicit a revertant or partially revertant phenotype. But suppressor mutations can be genetically separated, by recombination, from the mutations that they suppress. This review is intended as a supplement to some condensed reviews and more recent extensive summaries restricted to aspects of informational suppression. The purpose of this chapter is to describe systems that seem to be informative and/or illustrative of types, of suppressor activity. It also highlights that suppressor analysis can yield insight into arrays of problems, not readily subject to more classic genetic experimentation. Contributions to genetics and the resolving power of suppressor studies also are discussed in this chapter.

Mechanisms of Suppression

Salmonella typhimurium derepressed for the histidine biosynthetic enzymes form wrinkled colonies at 37 °C on media containing a high (2%) content of metabolizable carbon source. "Wrinkledness" reflects accumulation of multinucleate filamentous cells caused by impaired cell division. At 42 °C, DNA synthesis and nuclear division are impaired. Addition of methionine at 42 °C permits DNA synthesis, nuclear division, and, under some conditions, cell division. However, multinucleate filaments are formed both on high and on low carbon source at 42 °C. The filaments contain nuclei that are peculiarly hypersensitive to inactivation with ultraviolet (uv.) light.Overproduction of both the hisH and hisF gene products is required for these pleiotropic effects of derepression. The hisH and hisF proteins, and even some of their enzymologically inactive forms, may cooperate to inhibit cell division by direct interaction with (a) sensitive cellular site(s).

Philip E. Hartman

Papers

Overproduction of hisH and hisF gene products leads to inhibition of cell cell division in Salmonella.