J. Biol. Chem., Vol. 261, Issue 23, 10637-10645, Aug, 1986
DNA ligase from Drosophila melanogaster embryos. Purification and physical characterization
BA Rabin, RS Hawley and JW Chase
A DNA ligase has been purified approximately 2,100-fold, to near-
homogeneity, from Drosophila melanogaster 6-12-h embryos and was shown to
catalyze the formation of 3',5'-phosphodiester bonds. Polypeptides with
molecular weights 83,000, 75,000, and 64,000 were observed when the
purified enzyme was electrophoresed under denaturing conditions. These
polypeptides were shown by partial proteolysis studies and two- dimensional
gel analysis to be structurally related. The two smaller polypeptides were
presumably derived from the largest, 83,000 molecular weight protein, by
proteolysis during purification or in vivo. All three polypeptides formed
enzyme-adenylylate complexes in the absence of DNA. Drosophila DNA ligase
had a Stokes radius of 45 A, a sedimentation coefficient of 4.3 S, and a
frictional ratio of 1.6, yielding a calculated molecular weight of 79,800.
These studies indicate that DNA ligase from Drosophila embryos is a
monomer. The purified ligase was free of detectable ATPase, nuclease,
topoisomerase, and DNA polymerase activities. The enzyme exhibited an
absolute requirement for ATP in the joining reaction. A divalent metal was
required and N-ethylmaleimide inhibited the reaction. Formation of
phosphodiester bonds by Drosophila ligase required the presence of 5'-
phosphoryl and 3'-hydroxyl termini. The purified enzyme restored biological
activity to endonucleolytically cleaved pBR322 DNA. The specific activity
of Drosophila DNA ligase was highest in unfertilized eggs. Developing
embryos had 5-10-fold more ligase activity than at any later time in
development.