Nucleotide cell mutants

Meyer PR, Matsuura SE, Mian AM, So AG, Scott WA (1999) A mechanism of AZT resistance an increase in nucleotide-dependent primer unblocking by mutant HIV-1 reverse transcriptase. Mol Cell 4 35 3... 

A variety of mammalian cell culture systems can be used to detect mutations induced by chemical substances. The L5178Y mouse l)nnphoma line, measuring mutation at the TK locus, is preferred. TK is an important enz)une involved in DNA synthesis. Cells are exposed to the test substance at various concentrations, in the presence and absence of a metabolic activation system, for a suitable period of time, and then subcultured to assess cytotoxicity and to allow phenotypic expression prior to mutant selection. Cells deficient in TK because of a forward mutation are resistant to the cytotoxic effects of pyrimidine analogues (antimetabolites), such as trifluorothymidine (TFT). This is because the antimetabolites cannot be incorporated into cellular nucleotides and kill the cell through inhibition of cellular metabolism. After treatment, cells are grown in a medium containing TFT mutant cells can proliferate in the presence of TFT, whereas normal cells containing TK are killed. This allows the detection of an increase in mutant... 

The occurrence of this group of sugar nucleotides is limited mainly to the cells of Gram-negative bacteria. Those bacterial mutants defective in lipopolysaccharide synthesis are useful for preparative isolation of such esters, as the concentration of sugar nucleotides in normal cells is very low. 

Nucleotide Biosynthesis in Amino Acid Auxotrophic Bacteria Normal E. coli cells can synthesize all 20 common amino acids, but some mutants, called amino acid aux-otrophs, are unable to synthesize a specific amino acid and require its addition to the culture medium for optimal growth. Besides their role in protein synthesis, some amino acids are also precursors for other nitrogenous cell products. Consider the three amino acid auxotrophs that are unable to synthesize glycine, glutamine, and aspartate, respectively. For each mutant, what nitrogenous products other than proteins would the cell fail to synthesize ... 

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