PREPARATION AND PROPERTIES OF NATIVE CRAB dAT

Abstract

A procedure for the separation of native DNA''s with different base compositions by selective complexing with Hg++ or Ag++ and density gradient centrifugation in Cs2SO4 is described. Cancer crab dAT binds Hg++ more strongly than does the main component of crab DNA; the reverse is true for Ag+. The properties of the dAT obtained by this procedure indicate that it is truly native, that is, it has the same properties as this com- ponent in whole crab DNA. The crab dAT obtained by the procedure of heating and cooling whole crab DNA, followed by MAK column chromatog-raphy, is not completely native. Evidence for this on the basis of optical melting profiles, electron microscopy, the rate of attack by E. coli exonuclease I, electrophoresis, and buoyant density is offered. On heating and cooling, synthetic dAT renatures much more completely than crab dAT by the above criteria. Thus, the GC content of the crab dAT is responsible for its incomplete renaturability.