Yeast tryptophan synthetase

Fig. 3. Sephadex GlOO elution profiles showing the relative positions of yeast wild-type and trpS mutant enzyme activities. The first panel shows the relative positions at which the wild-type yeast tryptophan synthetase, assayed for reactions A and B, elutes from the column. The position at which E. coli A protein elutes is included for comparison. The nonsense mutants trS-3 and trS-9 gave the same elution profiles as tr5-35. The wild-type protein has a molecular weight of 160,000 and is excluded by the column. The fragment synthesized in nonsense mutants has a molecular weight of 35,000 and is retarded by the column.

Biocatalytic C-C-formatiou BY and other yeasts, AcCoA AcCoA C-acetyltrans-ferase, tryptophan synthetase, prenyltransferase, oxynitrilases, aldolases, transketolases, sterol cyclase... 

It is not yet possible to decide whether or not the trp5 region is an operon. If it were, then the lU and lA regions would represent two adjacent cistrons. This question will be answered experimentally by showing whether the tryptophan synthetase is composed of one or two polypeptides. The regulation of the yeast trypotophan synthetase activity is clearly different from that of the E. coli enzyme. The levels of the yeast complex do not appear to be derepressed or repressed by changes in the intracellular concentration of tryptophan [40]. In fact, the enzyme levels may be controlled by a protease [41]. 

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