A 2 kb DNA fragment, containing the photoreactivation gene phr1 from Escherichia coli, was inserted at the BamH1 site in the tet gene of the yeast - E. coli shuttle vector pJDB207. Photoreactivation - deficient Saccharomyces cerevisiae cells transformed with this plasmid showed photoreactivation of killing after UV irradiation of the cells, while extracts of transformed cells exhibited photoreactivating activity in vitro. Far more photoreactivating enzyme molecules were found when the gene was inserted in the plasmid in the opposite orientation to the tet gene as compared with a plasmid carrying the inserted gene in the same orientation. Photoreactivating enzyme encoded by the E. coli phr1 gene and produced in transformed yeast cells has characteristics of the E. coli photoreactivating enzyme (flavoprotein) as judged from the influence of ionic strength on photoreactivating activity.
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