Gene 6 Exonuclease of Bacteriophage T7

Abstract

Abstract We have investigated the mechanism of action of the gene 6 exonuclease of bacteriophage T7. The enzyme hydrolyzes duplex DNA until about 50% of the DNA is acid soluble. The remaining acid-insoluble DNA is single stranded and the acid-soluble product is almost entirely 5'-mononucleotides. The enzyme begins its exonucleolytic attack at the 5' terminus of DNA and hydrolyzes 5'-phosphoryl terminated and 5'-hydroxyl terminated DNA at equal rates. The exonuclease releases a dinucleoside monophosphate from a 5'-hydroxyl terminus and is able to release from one chain of DNA and begin hydrolysis of another before completion of hydrolysis. The enzyme is able to initiate hydrolysis at nicks as well as at external termini. The gene 6 exonuclease is involved in the acid solubilization of bacterial DNA after T7 phage infection. The enzyme may also be involved in other processes such as genetic recombination.