REVERSAL OF MUTANT PHENOTYPES BY 5-FLUOROURACID: AN APPROACH TO NUCLEOTIDE SEQUENCES IN MESSENGER-RNA

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Abstract
5-Flourouracil partially reverses the defective phenotypes of certain rII mutants of phage T4 (as well as certain phosphatase-negative mutants of E. coli). From the kinetics of the effect and the specificty of action on various rII mutants, taken together with the responses of the mutants of specific mutagens, it is concluded that 5FU acts mainly by incorporation into messenger-RNA in place of uracil, there acting partially like cytosine. The results are consistent with the idea that only one strand of the DNA duplex is copied into useful messenger-RNA. This provides a means for determining the orientation of the nucleotide pairs with respect to the two DNA chains, as well as identification of the nuclootides at the corresponding sites in the rII messenger-RNA.