Purification and certain properties of exonuclease A of bacteriophage T4

Exonuclease A was isolated from E. coli cells infected with bacteriophage T4. The molecular weight of the enzyme was equal to -42,000, optimum pH 7-8.5, pI 4.05. The activity of the enzyme depends on Mg super(2+) ions, the optimum concentration of which is 1-5 mM. Exonuclease A cleaves single-stranded and double-stranded DNA in the 3' arrow right 5' direction and is deoxyriboexonuclease, which splits out 5'-deoxynucleotides. The enzyme possesses almost the same affinity for single-stranded and double-stranded DNA. Exonuclease A can be used in the preparation of substrates for DNA polymerase T4 and the Klenow fragment, i.e., in the case of labeling of DNA on the 3'-ends.