Nucleic Acids Research, Vol 24, Issue 12 2281-2287, Copyright © 1996 by Oxford University Press
AJ Doherty, SR Ashford and DB Wigley
Treatment of T7 DNA ligase with a range of proteases generates two major
fragments which are resistant to further digestion. These fragments, of
molecular weight 16 and 26 kDa, are derived from the N- and C-termini of
the protein, respectively. The presence of ATP or a non-hydrolysable
analogue, ADPNP, during limited proteolysis greatly reduces the level of
digestion. The N-terminal 16 kDa region of the intact T7 ligase is labelled
selectively in the presence of [alpha- 32P]ATP, confirming that it contains
the active site lysine residue. In common with the intact enzyme, the
C-terminal portion of the protein retains the ability to band shift DNA
fragments of various lengths, implicating it in DNA binding. It can also
inhibit ligation by the intact protein, apparently by competing for target
sites on DNA. We conclude that the N-terminal region, which contains the
putative active site lysine, plays a role in the transfer of AMP from the
enzyme- adenylate complex to the 5'phosphate at the nick site, while the C-
terminal 26 kDa fragment appears to position the enzyme at the target site
on DNA.
ARTICLES
Characterization of proteolytic fragments of bacteriophage T7 DNA ligase
Laboratory of Molecular Biophysics, University of Oxford, UK.
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