J Biol Chem 247: 224-31 (1972)[72157909]
Proteolysis of Escherichia coli DNA polymerase (mol wt 109,000)
yields two fragments: a large fragment (mol wt 76,000) which retains
polymerase and 3' => 5' exonuclease activities, and a small
fragment (mol wt 36,000) which retains only the 5' => 3'
exonuclease activity. The large fragment has been obtained in two
ways: by cleavage of the intact enzyme with subtilisin or other
proteases, and by isolation from E. coli extracts, presumably after
proteolysis had occurred in the extract. The large fragment carries
out DNA synthesis on nicked double-stranded DNA without degradation
of the strand ahead of the growing point, and catalyzes a 3' => 5'
exonuclease action on both single- and double-stranded DNA with
production of nucleoside monophosphates. The large fragment is
inactive in unprimed poly[d(A - T)J synthesis, but catalyzes
primed poly[d(A - T)] synthesis at a relatively linear rate
generating poly[d(A-T)] molecules up to 10 micro-m in length.
The single cysteine residue and the single disulfide group of the
intact enzyme are retained in the large fragment as are the binding
sites for a deoxyribonucleoside triphosphate and a 3'-hydroxyl
ribonucleotide (primer terminus).
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