Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The enzyme activities specified by the tyrA and pheA genes were studied in wildtype strain Salmonella typhimurium and in phenylalanine and tyrosine auxotrophs. As in Aerobacter aerogenes and Escherichia coli, the wild-type enzymes of Salmonella catalyze two consecutive reactions: chorismate --> prephenate --> 4-hydroxy-phenylpyruvate (tyrA), and chorismate --> prephenate --> phenylpyruvate (pheA). A group of tyrA mutants capable of interallelic complementation had altered enzymes which retained chorismate mutase T activity but lacked prephenate dehydrogenase. Similarly, pheA mutants (in which interallelic complementation does not occur) had one group with altered enzymes which retained chorismate mutase P but lacked prephenate dehydratase. Tyrosine and phenylalanine auxotrophs outside of these categories showed loss of both activities of their respective bifunctional enzyme. TyrA mutants which had mutase T were considerably derepressed in this activity by tyrosine starvation and consequently excreted prephenate. A new and specific procedure was developed for assaying prephenate dehydrogenase activity.
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PMID:Enzyme alterations in tyrosine and phenylalanine auxotrophs of Salmonella typhimurium. 494 89

Wild-type Brevibacterium flavum has been shown to possess arogenate dehydrogenase activity and to lack prephenate dehydrogenase, thereby providing presumptive evidence that arogenate (previously named "pretyrosine") is an obligatory intermediate of L-tyrosine biosynthesis. A similar enzymological pattern has been discerned in extracts made from wild-type cultures of various species of cyanobacteria. Application of rigorous molecular genetic criteria in confirmation of the exclusive role of arogenate in L-tyrosine synthesis was made possible by the isolation of an auxotrophic mutant exhibiting a nutritional requirement for L-tyrosine. The mutant was found to lack activity for arogenate dehydrogenase and to accumulate substantial amounts of arogenate behind the mutant block during starvation for L-tyrosine.
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PMID:Arogenate (pretyrosine) is an obligatory intermediate of L-tyrosine biosynthesis: confirmation in a microbial mutant. 692 82

When 3 x 10(8) bacteria of the Escherichia coli tyrA14(oc) leu308(am) strain WU3610 are plated on glucose salts agar supplemented with leucine only, colonies of slow-growing Tyr+ suppressor mutants begin to appear after about a week and increase in numbers roughly linearly with time thereafter (stationary phase or starvation-associated mutation). From a library constructed from two of these mutants, a clone was obtained that suppressed the tyrosine requirement of WU3610 when present on a multicopy plasmid. The activity was identified to an open reading frame we call tas, the sequence for which has homology with a variety of known genes with aldo-keto reductase activity. The activity of tas complements the prephenate dehydrogenase dysfunction of tyrA14 (the chorismate mutase activity of tyrA possibly being still functional). A strain deleted for tas showed no spontaneous mutation under starvation conditions. Whereas neither tas+ nor tas bacteria showed any increase in viable or total count when plated under conditions of tyrosine starvation at 3 x 10(8) cells per plate, at lower density (approximately 10(7) per plate) tas+ but not tas bacteria showed considerable residual growth. We suggest that the single copy of tas present in WU3610 allows cryptic cell or DNA turnover under conditions of tyrosine starvation and that this is an essential prerequisite for starvation-associated mutation in this system. The target gene for mutation is not tas, although an increase in the expression of this gene, for example, resulting from a suppressor mutation affecting supercoiling, could be responsible for the slow-growing Tyr+ phenotype.
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PMID:Reversion of the tyrosine ochre strain Escherichia coli WU3610 under starvation conditions depends on a new gene tas. 956 Mar 82