Requirement of a Phage-Induced 5′-Exonuclease for the Expression of Late Genes of Bacteriophage T5

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Abstract
Amber mutants of bacteriophage T5 defective in gene D15, which codes for a 5'-exonuclease, do not express late genes. Electrophoretic separation in sodium dodecyl sulfate-polyacrylamide gels of the proteins induced by this mutant in nonpermissive Escherichia coli show a virtual absence of late proteins. Synthesis of lysozyme and serum-blocking power is very low whereas the extent of synthesis of an early enzyme, deoxyribonucleoside monophosphokinase, is similar to that in wild-type infections. It is proposed that one requirement for the expression of late T5 genes is the introduction of gaps or nicks in the T5 DNA so that late transcription can occur.