Biosynthesis of the branched-chain amino acids in yeast: a trifluoroleucine-resistant mutant with altered regulation of leucine uptake.
A trifluoroleucine-resistant mutant of yeast has been isolated that exhibits reduced incorporation of the analogue into protein (15%) of that in the wild type. In the mutant, uptake of the analogue and leucine into the expandable (water-extractable) pool is enhanced, passage from the expandable to the conversion (nonwater-, ethanol-extractable) pool is unaffected, and endogenous synthesis of leucine is normally regulated. Although the leucyl transfer ribonucluic acid (tRNA) synthetase appears normal, and the tRNA(leu) has wild-type acceptor activities in vitro and in vivo, the level of the mutant trifluoroleucyl tRNA pool is only 2 to 3% of that in the wild type. The data support the idea of a mutation affecting passage between the conversion pool and the site of charging of the analogue. The mutation is dominant and exhibits pleiotropic effects: the first leucine biosynthetic enzyme appears nonrepressible, and the leucine, valine, and tyrosine uptake systems are constitutively elevated (three- to fourfold) in the absence of exogenous amino acids.
D000596:Amino Acids / Q000096:biosynthesis / Q000302:isolation & purification; D002247:Carbon Isotopes; D005461:Fluorine / Q000096:biosynthesis; D007930:Leucine / Q000096:biosynthesis*; D008190:Lyases / Q000378:metabolism; D009154:Mutation; D012343:RNA, Transfer / Q000378:metabolism; D012440:Saccharomyces / Q000201:enzymology / Q000378:metabolism*
D000596:Amino Acids; D002247:Carbon Isotopes; D005461:Fluorine; D012343:RNA, Transfer; D008190:Lyases; D007930:Leucine