Mutants conditionally lethal

Pringle J.R. (1978) The use of conditional lethal cell cycle mutants for temporal and functional sequence... 

Temperature-sensitive mutations are those which allow a virus to replicate at one temperature and not at another, due to a mutational alteration in a virus protein that renders the protein unstable at moderately high temperatures. For instance, temperature-sensitive mutants are known in which the phage will not be replicated in the host at 43 °C but will at 25 °C, although the host functions at both temperatures. Such mutations are called conditionally lethal, since the virus is unable to reproduce at the higher temperature, but replicates at the lower temperature. 

Stansfield 1, Jones KM, Kushnirov VV, Dagkesamanskaya AR, Poznyakovski Al, Paushkin SV, Nierras CR, Cox BS, Ter-Avanesyan MD, Tuite ME (1995) The products of the SUP45 (eRFl) and SUP35 genes interact to mediate translation termination in Saccharomyces cerevisiae. EMBO J 14 4365 373 Stansfield 1, Eurwilaichitr L, Akhmaloka, Tuite ME (1996) Depletion in the levels of the release factor eRFl causes a reduction in the efficiency of translation termination in yeast. Mol Microbiol 20 1135-1143 Stansfield 1, Kushnirov VV, Jones KM, Tuite ME (1997) A conditional-lethal translation termination defect in a sup45 mutant of the yeast Saccharomyces cerevisiae. Fur J Biochem 245 557-563 Stark H (2002) Three-dimensional electron cryomicroscopy of ribosomes. Curr Protein Pept Sci 3 79-91... 

M Karita, ML Etterbeek, MH Forsyth, MK Tummuru, MJ Blaser. Characterization of Helicobacter pylori dapE and construction of a conditionally lethal dapE mutant. Infect Immun 65 4158-4164, 1997. 

SS Eveland, DL Pompliano, MS Anderson. Conditionally lethal Escherichia coli murein mutants contain point defects that map to regions conserved among murein... 

Other important questions remain to be solved are the single monomeric DNA polymerases detected in different species unique or do they correspond to a predominant activity in vitro which hides the activities of one or several other DNA polymerases (as DNA polymerase I hides DNA polymerases 11 and 111 in eubacteria) does this monomeric DNA polymerase correspond to a replicase (or to the catalytic subunit of a replicase complex), or to a repair enzyme The in vitro study of the replication of an extrachromosomal DNA would be useful for such investigations, but a definitive answer would require the isolation of conditionally lethal mutants. 

Temperature-sensitive ts) mutants have proven to be the most useful type of mutants for a number of viruses and bacteria because of their conditional-lethal phenotype. The (ts) mutants are produced by alteration in the nucleotide sequence of a gene so that the resulting protein product of the gene is unable to assume or maintain its functional configuration at the non-permissive (37-39°C) temperature. The protein, however, is able to assume a functional configuration at the permissive temperature (32-34° C), e.g., herpesviruses, adenoviruses, and influenza viruses. Thus, these mutants can replicate in mucosal sites with a lower temperature, e.g., the nasal cavity, but are unable to cause systemic infections and disease. 

The fundamental enzymology of DNA replication derives from both in vivo and in vitro studies with cells and extracts derived from E. coli. Many of the enzymes involved in DNA replication were identified by isolation of conditional lethal mutants of the bacterium, e.g., mutants that are unable to replicate DNA (and unable to grow) at high temperatures (42°C) but that replicate and grow normally at low temperatures (30°C). 

Eveland, S.S., Pompliano, D.L., and Anderson, M.S. (1997) Conditionally lethal Escherichia coli murein mutants contain point defects that map to regions conserved among murein and folyl poly-y-glutamate ligases identification of a ligase superfamily. Biochemistry, 36, 6223-6229. 

Nutritional auxotrophs can be described as conditionally lethal mutants they survive only if the medium is supplemented with the nutrient, whose S5mthesis depends upon the missing enzyme. Other kinds of conditional lethal mutations permit study of almost every gene in an organism. For example, temperature-sensitive (fs) mutants grow perfectly well at a low temperature, e.g., 25°C, but do not grow at a higher temperature, e.g., Many... 

The replica-plating method may be used to select many types of mutants for which it would be tedious and inefficient to screen individually. The more common application is to isolate auxotrophic, radiation-sensitive, and conditional-lethal mutants. The so-called conditional-lethal mutants are those which, because they are defective in some manner, survive and grow under permissive conditions but perish under restrictive conditions. 

Zhang, Y. and Moss, B. (1991) Inducer-dependent conditional lethal mutant animal viruses. Proc. Natl. Acad. Sci. USA 88,1511-1515. 

The study of the mechanism of assembly of a phage particle was first approached with coliphage T4 making use of the electron microscope and conditional lethal mutants. > Since then, the most studied phages, among those that contain double-stranded DNA, have been T4, lambda and P22. 

Only early RNA is made during infection with gene O conditional lethal mutants. Thus, the gene O product is necessary for transcription of late genes. We have not yet been able to identify protein pO, either because the nonsense fragment is very close to the C-terminal end or because protein pO overlaps with other protein band. In any case, protein pO is not a polymerase similar to the T7-induced RNA polymerase because, in contrast to T7, all 29-specific RNA synthesis is sensitive to rifamycin throughout the development cycle. Since the subunit of the host polymerase is the site of rifamycin sensitivity, this subunit must be necessary for all phage RNA synthesis. Extensive studies in our laboratory on... 

Obijeski, J. F., and Simpson, R. W., 1974, Conditional lethal mutants of vesicular stomatitis virus. II. Synthesis of virus-specific polypeptides in nonpermissive cells infected with RNA host-restricted mutants. Virology 57 369. 

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