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Expression of the tryptophan operon in merodiploids ofEscherichia coli

I. Gene dosage, gene position and marker effects

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Summary

Under conditions of derepression,Escherichia coli K12 strains diploid for thetrp operon specify more than twice as much enzyme as a haploid. The disproportionate increase probably occurs because episomally carriedtrp genes tend to specify more enzyme than do chromosomal genes.

Operons harboring the nonsense mutationtrpA2 or the missense mutationtrpBYS-101 specify less protein than do wild-type operons. This effect varies with operon location in the case oftrpBYS-101.

In a homozygoustrp merodiploid A46/F′ A46 reversion totrp + occurs three times as frequently in episomal DNA as in chromosomal DNA. Thus, if the chromosome: F′trp episome ratio inE. coli is one, as demonstrated by Helinski and co-workers, the rate of gene expression and the rate of mutation can vary and depends upon the location of the DNA within the cell.

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Author notes

  1. H. Stetson

    Present address: Division of Natural Sciences, Owosso College, Owosso, Michigan

Authors and Affiliations

  1. Department of Biochemistry, Purdue University, Lafayette, Indiana

    H. Stetson & R. L. Somerville

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  1. H. Stetson
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  2. R. L. Somerville
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Additional information

Communicated by W. Maas

Supported by Grant AM-12150 from the National Institutes of Health. Journal Paper No. 3973 of Purdue Agricultural Experiment Station.

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Stetson, H., Somerville, R.L. Expression of the tryptophan operon in merodiploids ofEscherichia coli . Molec. Gen. Genet. 111, 342–351 (1971). https://doi.org/10.1007/BF00569786

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  • DOI: https://doi.org/10.1007/BF00569786

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