Mutants sensitive

Certain ChE mutants sensitive to OPs do not age after phosphylation they are fully reactivatable (cf Figure 70.1, reaction 3). Such ChE mutants when associated with oximes (e.g. 2-PAM, HI-6) act as pseudocatalysts in displacing the OP moiety boimd to the enzyme. These enzyme-reactivator coupled systems could lead to a new family of pseudo-catalytic bioscavengers (Kovarik et al, 2007 Taylor et al, 2007). 

Stearns, T., M. A. Hoyt, and D. Botstein (1990). Yeast mutants sensitive to antimicrotubule drugs define three genes that affect microtubule function. Genetics 124, 251-262. 

When an acridonylalanine (acdAla) was incorporated at different positions of camel single-chain antibody against hen-lysozyme, the Tyrl06acdAla mutant sensitively responded to the binding of nanomolar concentration of the antigen, whereas the Trpl23acdAla mutant was insensitive to the binding (Fig. 5.1-16) [71]. When the same fluorescent amino acid was incorporated into streptavidin, some mutants responded to even a picomolar quantity of biotin [71]. The lower limit of the detectable concentration is determined not by the fluorescence sensitivity, but by the dissociation constants of the protein-small molecule interactions. 

Henriques, J. A. P., and Moustacchi, E. (1980). Isolation and characterization of pso mutants sensitive to photo-addition of psoralen derivatives in Saccharomyces... 

These restrictive conditions may include /)H, osmotic pressure, and temperature. This class of mutants is well known in microorganisms and insects and may well exist in manunalian cells. Recently, Naha (1969) reported the isolation of four different temperature-sensitive mutants in a hetero-nuclear monkey kidney cell line. In our laboratory, a number of temperature-sensitive mutants have been isolated by the replica-plating procedure (Chu and Smith, unpublished). Mutants sensitive to radiation or other adverse conditions may be similarly isolated and studied. 

Mutants sensitive to ultraviolet light or X-rays cf. Cox and Parry can show in many cases a cross-sensitivity to chemical mutagens. 

Okubo, S., Romig, W. R. Comparison of ultraviolet sensitivity of Bacillus subtilis bacteriophage SP02 and its infectious DNA. J. molec. Biol. 14, 130-142 (1965)-Okubo, S., Romig, W. R. Impaired transformability of Bacillus subtilis mutant sensitive to mitomycin C and ultraviolet radiation. J. molec. Biol. 15, 440-454 (1966). 

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

The first hormonal signal found to comply with the characteristics of both a satiety and an adiposity signal was insulin [1]. Insulin levels reflect substrate (carbohydrate) intake and stores, as they rise with blood glucose levels and fall with starvation. In addition, they may reflect the size of adipose stores, because a fatter person secretes more insulin than a lean individual in response to a given increase of blood glucose. This increased insulin secretion in obesity can be explained by the reduced insulin sensitivity of liver, muscle, and adipose tissue. Insulin is known to enter the brain, and direct administration of insulin to the brain reduces food intake. The adipostatic role of insulin is supported by the observation that mutant mice lacking the neuronal insulin receptor (NDRKO mice) develop obesity. 

Here, one mutated subunit is sufficient to strongly reduce ATP sensitivity thereby inducing additional symptoms in extrapancreatic tissues. To date two mutants within SlIRl are known (11424V and HI 023Y), resulting in hyperactive channels and PNDM. 

In cerebellar Purkinje cells, a TTX-sensitive inward current is elicited, when the membrane was partially repolarized after strong depolarization. This resurgent current contributes to high-frequency repetitive firing of Purkinje neurons. The resurgent current results from open channel block by the cytoplasmic tail of the (34 subunit. The med Nav 1.6 mutant mice show defective synaptic transmission in the neuromuscular junction and degeneration of cerebellar Purkinje cells. 

Palese P, Tobita K, Ueda M, Compans RW (1974b) Characterization of temperature sensitive influenza virus mutants defective in neuraminidase. Virology 61 397 10 Pegg MS, von Itzstein M (1994) Slow-binding inhibition of sialidase from influenza virus, Biochem Mol Biol Int 32 851-858... 

Although the NNRTIs target HIV-1 RT, they are clearly different from the nucleoside RT inhibitors (NRTIs). They are highly selective for HlV-1 and do not inhibit HlV-2 or any other retrovirus. Moreover, the resistance spectrum of NNRTIs is different from that of NRTI, and, as a rule, NRTl-resistant mutant virus strains keep full sensitivity to the inhibitory effects of NNRTIs, and NNRTI-resistant mutant virus strains keep full sensitivity to the inhibitory effects of NRTIs. However, some influence of NRTI mutations on NNRTl susceptibility has been observed (Shuhnan etal. 2004). 

Arion D, Kaushik N, McCormick S, Borkow G, Parniak MA (1998) Phenotypic mechanism of HIV-1 resistance to 3 -azido-3 -deoxythymidine (AZT) increased polymerization processivity and enhanced sensitivity to pyrophosphate of the mutant viral reverse transcriptase, Biochem 37 15908-15917... 

Changes in human immunodeficiency vims type 1 Gag at positions 1449 and P453 are linked to I50V protease mutants in vivo and cause reduction of sensitivity to amprenavir and improved viral fitness in vitro. J Virol 76 7398-7406... 

The development of resistance against HCV NS3/4 protease inhibitors will become a major challenge for the clinical use of these new compounds. Clinical trials of telaprevir (VX-950) have shown that mutations at different positions are rapidly selected (Sarrazin et al. 2005). In vitro studies indicate that cells bearing repUcons with those mutations are associated with different levels of resistance to telaprevir (< 10-fold change to >40-fold change in sensitivity). However, telaprevir-resistant mutants remain susceptible to interferon-a, at least in the replicon system. Likewise, replicon mutants that are resistant to boceprevir are still sensitive to interferon-a (Tong et al. 2006). 

Using a random mutagenesis approach, respiratory-deficient (34) and temperature-sensitive (46, 47) mutants of the Rieske protein of the yeast bc complex have been selected. A large fraction of the point mutants had changes of residues in the bottom of the cluster binding subdomain (the loop /S7-/38) and in the Pro loop comprising residues 174-180 of the ISF (Fig. 9 see Section III,B,3) this indicates the importance of the Pro loop for the stability of the protein. Amino... 

Behn M., Schuermann M. Sensitive detection of p53 gene mutations by a mutant-enriched PCR-SSCP technique. Nucleic Acids Res. 1998 26 1356-1358. 

A shift in temperature from 38 to 22 °C leads to desaturation of fatty acids in Anabaena variabilis [110], resulting in control of the fluidity of the plasma membrane. Mutants have been isolated in Synechocystis PCC 6803 that were defective in desaturation of fatty acids, and the growth rate of one of these mutants was much lower than that of the wild-type at 22 °C [112]. It turned out that the mutant strain had a mutation in the gene desA, and when the wild-type allele was introduced into the chilling-sensitive cyanobacterium Anacystis nidulans, it resulted in increasing the tolerance of that strain to low temperature [113]. These experiments nicely demonstrate the existence of a mechanism of adaptation to low temperature in a chilling-tolerant cyanobacterium. 

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