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|Title:||Aromatic catabolism of Escherichia coli: Regulation of the uptake and catabolism of hydroxyphenylacetate.|
|Authors:||Skinner, Michael Anthony.|
|Presented at:||University of Leicester|
|Abstract:||The organisation and regulation of the genes encoding the proteins for uptake and catabolism of hydroxyphenylacetate by Escherichia coli, has been studied. h3- and 4- Studies with hydroxyphenylacetate-negative mutants indicated that hydroxyphenylacetate induces only hydroxyphenylacetate uptake and hydroxylation. 3,4- ihydroxyphenylacetate induces the enzymes for the catabolism of 3,4-dihydroxyphenylacetate to pyruvate and succinate semialdehyde whilst succinate semialdehyde induces the succinate semialdehyde dehydrogenase. A brief study of hydroxyphenylacetate uptake, undertaken to help characterise hydroxyphenylacetate hydroxyhlase mutants, indicated that hydroxyphenylacetate is taken up by an active-transport process, probably of the "osmotic shock-sensitive" type. One mutant, defective in the NAD-dependent succinate semialdehyde dehydrogenase, was unable to grow on hydroxyphenylacetate due to the accumulation of succinate semialdehyde. Positive selection of secondary mutants, from the succinate semialdehyde dehydrogenase mutant, allowed isolation of mutations in the early enzymes of hydroxyphenylacetate catabolism. One secondary mutant, isolated following mutagenesis by Tn5, was non-inducible for hydroxyphenylacetate uptake and catabolism. A mutation causing constitutive synthesis of the 3,4-dihydroxyphenylacetate dioxygenase and subsequent enzymes was cis-recessive to the non-inducible hydroxyphenylacetate mutation and was trans-recessive to the inducible allele carried on an F prime. The genes encoding the hydroxyphenylacetate catabolic enzymes (the hpa genes) are located between minutes 1 and 3 on the Escherichia coli C chromosome. The hydroxyphenylacetate mutations isolated are 90% co-transducible with each other. Escherichia coli K-12 neither grows on hydroxyphenylacetate nor does it appear to carry any of the hpa genes. Transduction of the hpa genes from Escherichia coli C to Escherichia coli K-12 resulted in the hpa genes integrating at two positions on the chromosome. The hydroxyphenylacetate-positive Escherichia coli K-12 strains express the hydroxyphenylacetate permease and catabolic enzymes. The NAD-dependent succinate semialdehyde dehydrogenase was not co-transducible with the hpa genes. The equivalent Escherichia coli K-12 gene (sad) mapped at minute 34.1. A model is proposed for the regulation of synthesis of the hydroxyphenylacetate permease and catabolic enzymes.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Biochemistry|
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