1887

Abstract

Genetic evidence suggests that the activity of the native QUTA transcription activator protein is negated by the action of the QUTR transcription repressor protein. When was transformed with plasmids containing the wild-type gene, transformants that constitutively expressed the quinate pathway enzymes were isolated. The constitutive phenotype of these transformants was associated with an increased copy number of the transforming gene and elevated mRNA levels. Conversely, when was transformed with plasmids containing the gene under the control of the constitutive promoter, transformants with a super-repressed phenotype (unable to utilize quinate as a carbon source) were isolated. The super-repressed phenotype of these transformants was associated with an increased copy number of the transforming gene and elevated mRNA levels. These copy-number-dependent phenotypes argue that the levels of the QUTA and QUTR proteins were elevated in the high-copy-number transformants. When diploid strains were formed by combining haploid strains that contained high copy numbers of either the gene (constitutive phenotype) or the gene (super-repressing; non-inducible phenotype), the resulting diploid phenotype was one of quinate-inducible production of the quinate pathway enzymes, in a manner similar to wild-type. The simplest interpretation of these observations is that the QUTR repressor protein mediates its repressing activity through a direct interaction with the QUTA activator protein. Other possible interpretations are discussed in the text. Experiments in which truncated versions of the QUTA protein were produced in the presence of a wild-type QUTA protein indicate that the QUTR repressor protein recognizes and binds to the C-terminal half of the QUTA activator protein.

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1996-06-01
2021-10-25
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