Incorporation of uracil- 14C into nucleic acids in Escherichia coli infected with bacteriophage T4 and T4 amber mutants

Abstract

The synthesis of nucleic acids in Escherichia coli B infected with bacteriophage T4 and T4 amber mutants corresponding to twenty-one different genes has been investigated by following uracil- 14C incorporation into RNA and DNA. The results on DNA synthesis indicate that seven amber mutants previously classified as unable to induce phage DNA synthesis (DO mutants) actually induce significant incorporation of radioactivity from uracil- 14C into DNA in the restrictive host, indicating that some DNA synthesis must be occurring in these cells. Five of these were called DS mutants (some DNA synthesis), whereas the remaining could be classified as DD (delayed DNA synthesis), and DA (arrested DNA synthesis), in accordance with existing classifications. Five mutants are true DO mutants. The rate of net incorporation of radioactivity from uracil- 14C into RNA declines markedly 10 minutes after infection of E. coli B with DO mutants and is barely detectable by 20 minutes after infection. A significant portion of the RNA made early in the infection cycle is eventually degraded when RNA breakdown begins to exceed synthesis at about 10 minutes after infection. Nevertheless, these cells have previously been shown to maintain early enzyme synthesis for extended periods at near normal rates suggesting that the bulk of the RNA made early in infection is not messenger RNA for these early enzymes. Other types of mutants inducing defective DNA synthesis (delayed or arrested DNA synthesis or maturation defective) also show abnormal RNA profiles of various types. All mutants appeared to shut off host RNA synthesis. Uracil uptake by infected cells is strongly linked to nucleic acid synthesis in the cell. When net incorporation of uracil into nucleic acids ceases, uracil uptake also ceases, suggesting stringent control of nucleotide pool sizes in these infected cells.