5' leads to 3'-Exonucleases of bacteriophage T4.
Two enzyme activities which release nucleotides preferentially from the 5' termini of DNA were found in T4-infected Escherichia coli. Since no corresponding activities were found in uninfected cells, the activities appeared to be induced by T4. Both activities are capable of excising pyrimidine dimers from ultraviolet-irradiated DNA which has been treated with T4 endonuclease V. One of the activities , referred to as T4 exonuclease B, was purified 400-fold from an extract of T4v 1- infected cells. The enzyme initiates hydrolysis of DNA specifically at the 5' termini to yield products which are mainly oligonucleotides of varying length. The hydrolysis reaction proceeds in a limited manner. The enzyme shows optimal activity at pH 7.0 and absolutely requires Mg2+. The molecular weight of the enzyme , as estimated by gel filtration, is approximately 35,000. Another activity, referred to as T4 exonuclease C, was purified 240-fold from the extract. This activity also excises pyrimidine dimers from ultraviolet-irradiated, incised DNA and releases nucleotides at 5' termini. It has a pH optimum at 7.5 and requires Mg2+. The molecular weight of the enzyme is approximately 20,000.
D003090:Coliphages / Q000201:enzymology*; D004247:DNA / Q000528:radiation effects; D003851:Deoxyribonucleases / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004926:Escherichia coli / Q000201:enzymology*; D005092:Exonucleases / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D011830:Radiation Effects; D014466:Ultraviolet Rays
D004247:DNA; D003851:Deoxyribonucleases; D005092:Exonucleases; D008274:Magnesium