SP62 is a mutant of bacteriophage T4D that was discovered because it produces fewer phage than the wild type in the presence of
5-fluorodeoxyuridine. In the absence of phage
DNA synthesis, SP62 solubilizes host
DNA slower than normal; this may explain the sensitivity to
5-fluorodeoxyuridine. In Escherichia coli B at 37 C in the absence of drugs, SP62 makes
DNA at a normal rate and the kinetics of appearance of phage are nearly normal. Under the same conditions, SP62 produces T4
lysozyme (gene e) at a normal rate until 20 min, but then produces it at twice the normal rate until at least 60 min. It has long been known that, when T4
DNA synthesis is blocked (
DNA(-) state) in an otherwise normal
infection, the synthesis of a number of early
enzymes continues beyond the shutoff time of about 12 min seen in the
DNA(+) state, but still stops at about 20 min. We have termed the 12-min shutoff event S1 and the 20-min shutoff event S2. We show here that, in the
DNA(+) state, SP62 makes four early
enzymes normally, i.e., S1 occurs. However, in the
DNA(-) state (where S1 is missing), SP62 continues to make
dCTPase (gene 56),
dCMP hydroxymethylase (gene 42), and
deoxynucleotide kinase (gene 1) for at least an hour; this results in production of up to 13 times the normal level of
dCTPase at 60 min after
infection, or 6 times the
DNA(-) level. We conclude that SP62 is defective in the second shutoff mechanism, S2, for these three
enzymes. In contrast, SP62 causes premature cessation of
dTMP synthetase production in the
DNA(-) state; the result is a twofold underproduction of
dTMP synthetase. Autoradiograms of pulse-labeled
proteins separated by slab-gel electrophoresis in the presence of
sodium dodecyl sulfate show that a number of other T4 early
proteins, including the products of genes 45, 46, and rIIA, are synthesized longer than normal by SP62 in the
DNA(-) state. Few late
proteins are made in the
DNA(-) state, but in autoradiograms examining the
DNA(+) state there is little or no effect of the SP62 mutation on the synthesis of T4 late or early
proteins. Circumstantial evidence is presented favoring a role for the gene of SP62 in translation of certain mRNAs. At very high temperatures (above 43 C) in the absence of drugs, phage production, but not
DNA synthesis, is much reduced in SP62
infections relative to wild-type T4
infections; this temperature sensitivity is greater on E. coli CR63 than on E. coli B. This property has facilitated recognition of the SP62 genotype and aided in complementation testing and genetic mapping. A later publication will provide evidence that SP62 defines a new T4 gene named regA, which maps between genes 43 and 62.