Abstract
Mutations that alter the ebgA gene so that the evolved beta-galactosidase (ebg) enzyme of Escherichia coli can hydrolyze lactose fall into two classes: class I mutants use only lactose, whereas class II mutants use lactulose as well as lactose. Neither class uses galactosylarabinose effectively. In this paper we show that when both a class I and a class II mutation are present in the same ebgA gene, ebg enzyme acquires a specificity for galactosylarabinose. Although galactosylarbinose utilization can evolve as the consequence of sequential spontaneous mutations, it can also evolve via intragenic recombination in crosses between class I and class II ebgA+ mutant strains. We show that the sites for class I and class II mutations lie about 1 kilobase, or about a third of the gene, apart in ebgA. Implications of these findings with respect to the evolution of new metabolic functions discussed.
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- Bachmann B. J., Low K. B., Taylor A. L. Recalibrated linkage map of Escherichia coli K-12. Bacteriol Rev. 1976 Mar;40(1):116–167. doi: 10.1128/br.40.1.116-167.1976. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gall B. G., Hartl D. L. Regulation of newly evolved enzymes. II. The ebg repressor. Genetics. 1975 Nov;81(3):427–435. doi: 10.1093/genetics/81.3.427. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hall B. G., Clarke N. D. Regulation of newly evolved enzymes. III Evolution of the ebg repressor during selection for enhanced lactase activity. Genetics. 1977 Feb;85(2):193–201. doi: 10.1093/genetics/85.2.193. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hall B. G. Experimental evolution of a new enzymatic function. II. Evolution of multiple functions for ebg enzyme in E. coli. Genetics. 1978 Jul;89(3):453–465. doi: 10.1093/genetics/89.3.453. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hall B. G. Experimental evolution of a new enzymatic function. Kinetic analysis of the ancestral (ebg) and evolved (ebg) enzymes. J Mol Biol. 1976 Oct 15;107(1):71–84. doi: 10.1016/s0022-2836(76)80018-6. [DOI] [PubMed] [Google Scholar]
- Hall B. G., Hartl D. L. Regulation of newly evolved enzymes. I. Selection of a novel lactase regulated by lactose in Escherichia coli. Genetics. 1974 Mar;76(3):391–400. doi: 10.1093/genetics/76.3.391. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hall B. G. Number of mutations required to evolve a new lactase function in Escherichia coli. J Bacteriol. 1977 Jan;129(1):540–543. doi: 10.1128/jb.129.1.540-543.1977. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hartl D. L., Hall B. G. Second naturally occurring beta-galactosidase in E. coli. Nature. 1974 Mar 8;248(5444):152–153. doi: 10.1038/248152a0. [DOI] [PubMed] [Google Scholar]