Amber mutants

Immediately after its identification DNA polymerase I was generally assumed to be the principal chain elongation enzyme. However, an amber mutant of E. coli deficient in DNA polymerase I (gene polA ... 

As noted above amber mutants in gene 3 produce only limited amounts of DNA under restrictive conditions. It is therefore clear that degradation of host DNA is required for normal T7 DNA synthesis and phage production, a result which is to be anticipated in light of the finding that T7 derives most of its nucleotides from host nucleic acids (65). 

All test compounds were evaluated both in vitro and in vivo. The mouse was the animal chosen, although hamsters and rats have been successfully used. Frameshift, missense, ochre, and amber mutants were the indicators used. Table 1 lists the mutants used, their classification, and their deriva-... 

In addition to the G-46 missense mutant, the frameshift mutant C-207 and the amber mutant C-340 were evaluated. The results paralleled the previously reported in vitro findings. The increase in the number of... 

Amber mutants mutant bacteria in which the mRNA contains the codon UAG as a result of a point mutation (see Amber codon). The mutation is not necessarily lethal, because a compensatory suppressor mutation in a tRNA may enable the protein synthesizing system to recognize the amber codon as a sense codon. The term amber was arbitrarily chosen by the discoverer of A. m. 

Suppressor W6th reference to Amber mutants (see) and Ochre mutants (see), a S. mutation is a secondary mutation in a tRNA dstron, which restores the ability of the tRNA to recognize the nonsense codon. The resulting new tRNA is called suppressor tRNA. The nonsense codon then becomes a sense codon and codes for a specific proteogenic amino add during translation. 

Hausmann, R., Gomez, B. Amber mutants of bacteriophages T3 and T7 defective in phage-directed deoxyribonucleic acid synthesis. J. Virol. 1, 779-792 (1967). 

Morse, D. E., Yanofsky, C. Amber mutants of the trpR regulatory gene. J. molec. Biol. 44, 185-193 (1969). 

Sadowski, P. D., Kerr, C. Degradation of Escherichia coli B deoxyribonucleic acid after infection with deoxyribonucleic acid-defective amber mutants of bacteriophage T7. J. Virol. 6, 149-155 (1970). 

Kitamoto, T., Iizuka, R., and Tateishi.J. (1993). An amber mutation of prion protein in Gerstmann-Straussler syndrome with mutant PrP plaques. Biochem. Biophys. Res. Commun. 192, 525—531. 

This enzyme from E. coli is a tetramer of four identical subunits, each of molecular weight 116,500. Amber and ochre (premature termination) mutants of the enzyme provide a number of enzymically inactive, incomplete peptide chains, identical in sequence with the N-term nal part of the wild-type chains. A subset of these N-terminal peptides, called acceptor peptides, can combine with so-called wild-type chain, to restore enzymic activity (Ullmann et al., 1965, 1967 Ullmann and Perrin, 1970 see also the review by Zabin and Villarejo, 1975). Goldberg (1969) suggested that the acceptor peptides and the independent nucleation centers as evidenced by the following facts ... 

A mutant amber suppressor tRNA library based on the... 

The codons of individual tryptophan residues in the cloned a chain were exchanged for an amber stop codon (TAA) and the mutant mRNA was obtained by in vitro transcription. 

A comprehensive test of computational protocols applied for the short time dynamics of the photolysed Mb-CO complex is presented by Meller and Elber [110]. 270 different 10 ps molecular dynamics simulations were carried out using two different solvation boxes, two differenc types of electrostatic cutoffs and two different treatments of the photodissociated ligand. In addition, both the wild-type and the Leu29Phe mutant were treated. 9 different setups were combined from the variables described and 30 trajectories were generated for all. Results presented are averages over these 30 trajectories. Calculations were performed using a combination of the AMBER [111] and OPES [112] force fields, the heme model of Kuczera et al. [16] and approximately 2700 TIP3P... 

Atweh GF, Brickner HE, Zhu X-X, Kazazian HHJ, Forget BG New amber mutation in a b-thalassemic gene with nonmeasurable levels of mutant messenger RNA in vivo. J Clin Invest 82 557-561,1988. 

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