Adapted mutants

Evolutionary optimization then is not just a blind stochastic trial-and-error search for a better adapted mutant but rather follows an inherent logic ... 

Cold-adapted mutants Site-directed mutants Gene-deleted mutants Gene reassessment mutants Natiwally available mutants Mutants generated by adaptation to unnatural host... 

Adapted mutants Adapted mutants were selected by the natural screening of 0.5 x 10 5/ml conidia of P. oryzae and IK oryzae over the EDDP-amended medium. Colonies obtained thus on five times higher concentration of the ED5q dose of sensitive strain were further trained to grow on higher concentrations. 

Stable and virulent mutants For P. oryzae, one EMS (POLR-1), the adapted mutants (POLR-2 and POLR-3) and one UV mutant (POLR-4) and for D. oryzae, one EMS mutant (DOLR-1) and four field mutants (DOFR-1, DOFR-2, DOFR-3 and DOFR-4) were chosen based on their stability and pathogenicity. 

The results in Table V show that the chemical mutant of P. oryzae (POLR-1) was highly sensitive to Carbendazim, Ziram and Mercuric chloride. Adapted mutant POLR-2 was found sensitive to Bitertanol, ziram, and Mancozeb. The UV mutant POLR-4 was sensitive to Wettable sulphur, Ziram and Mancozeb. EMS mutant of 13. oryzae (DOLR-1) showed high sensitivity to Mancozeb and Bitertanol while the two resistant field strains (DOFR-1 and DOFR-2) were sensitive only to Mancozeb. The resistance level (Q value) was less than one for the above chemicals. 

Parkinson, J.S. and Revello, P.T. (1978). Sensory adaptation mutants oiEscherichia coli. Cell 15, 1221-1230. 

Butyribacterium methylotrophicum CO-adapted mutant strain CO 0.33 g/L Shenetal. (1999)... 

Figure 17.4 Melting temperatures, Tm, of engineered single-, double-, and tripledisulfide-containing mutants of T4 lysozyme relative to wild-type lysozyme. The red bars show the differences in Tm values of the oxidized and reduced forms of the mutant lysozymes. The green bars for the multiple-bridged proteins correspond to the sum of the differences in Tm values for the constituent single-bridged lysozymes. (Adapted from M. Matsumura et al.. Nature 342 291-293, 1989.)...

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. 

In the absence of suitable cell wall mutants, DCB-adapted tomato cells provide an opportunity to characterise the pectin network of the plant cell wall. It should be noted that synthesis and secretion of hemicellulose is not inhibited but, in the absence of a cellulose framework for it to stick to, most of the xyloglucan secreted remains in soluble form in the cells culture medium (9, 10) while other non-cellulosic polysaccharides and other uronic-acid-rich polymers predominate in the wall. 

Fig. 13 DNA-protein CT reactions. The DNA-bound protein, methyltransferase Hhal (mutant Q237W), flips a base out of the DNA double helix and inserts a trytophan side chain leaving the /r-stack largely unperturbed. This intercalated trytophan moiety transfers an electron to [Ru(bpy )(dppz)(phen)]3+, generated by flash quench, over 50 A away. Adapted from [164]... 

Pan, Y., Kislinger, T., Gramolini, A.O., Zvaritch, E., Kranias, E.G., MacLennan, D.H., Emih, A. (2004). Identification of biochemical adaptations in hyper- or hypocontractile hearts from phospholamban mutant mice by expression proteomics. Proc. Natl. Acad. Sci. USA 101, 2241-2246. 

Fig. 16. Phototropic threshold of wild type and hypothetical photoreceptor mutants. Solid line = wild type large dashes = mutant with reduced number of photoreceptor dotted line = mutant with reduced absorption cross-section small dashes = mutant with slow regeneration. The changes of threshold of the hypothetical mutants were chosen arbitrarily. The figure was adapted to Fig. 6 and the solid line of the wild type represent data of Foster and Lipson (1973)...

Among the many sensory reactions Phycomyces displays, the study of the photoreceptor and adaptation deserves maximal attention, since Phycomyces shares these two attributes with a variety of other blue light sensitive organisms. Action-spectroscopy indicates a flavin as the photoreceptor of Phycomyces. /3-carotene was positively ruled out as a possible receptor, since mutants with no trace amounts of )3-carotene are phototropical normal. The photoreceptor has not yet been isolated. As in other systems the difficulty consists in distinguishing the flavin photoreceptor from the bulk flavoproteins in the cell. One therefore needs unambiguous criteria for the identification of the photoreceptor. The most promising approach for an isolation would be a photoreceptor mutant and we described the properties those mutants should have. Until now there is no firm evidence that the photomutants, madA or madB are defective in the photoreceptor. 

Later steps after the adaptation output involve transient changes of cAMP levels and a mutant with a defect in the madD gene turned out to have an altered phosphodiesterase. This madD mutant is the first behavioral mutant of Phycomyces whose biochemical nature is known. 

Some of the molecules responsible for hair-cell transduction have been identified. A few key molecules, some already described, have been identified as part of the transduction complex (Fig. 51-6). Myosin molecules clearly play essential roles, and hair cells express a variety of myosin isoforms. Because it is located at the tips of the stereocilia, near the tip-link anchors, myosin-1 c is the best candidate for the adaptation motor. Selective inhibition of a sensitized myosin- lc mutant with an ADP analog proved that this myosin participates in adaptation [14], although contribution by other myosins has yet to be ruled out. For example, mice with near-null mutations in myosin-7a have defects in auditory transduction that are consistent with alterations in the adaptation machinery, suggesting a central role for this myosin too [15]. 

In actual research, setups developed for the analysis of Ras interaction are adapted for the screening of new therapeuticals, e. g., chemicals which overcome the lack in GAP-stimulated GTP-hydrolysis of oncogenic Ras mutants [35]. 

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