A difference in nucleic acid preparations from Ehrlich ascites nuclei and calf thymus nuclei

A COKSIDERARLE amount of attention has been directed by a number of investigators to the determination of the physical properties of deoxyribonucleic acid, DNA, isolated from normal tissues such as calf thymus. The purpose of this investigation is to characterize by physical and chemical methods deoxyribonucleic acid, DNA, from the neoplastic source, Ehrlich ascites cells. In the isolation procedures for DNA it is necessary to take precautions to avoid the Scylla of autolytic enzyme degradation and the Charybdis of other degradative factors such as extremes of pH, shearing stresses, temperature and excessive drying [4]. The majority of the samples which have been characterized by physical and chemical methods have been prepared from tissues or whole cells. Marham and Smith [8] have stated that nucleoproteins prepared from whole tissues without any attempt at separation of the nuclear and cytoplasmic components must be mixtures of riboand deoxyribonucleic acids. It is also possible that there can be contamination from other cytoplasmic constituents. In this laboratory an effective technique employing a high viscosity suspending medium such as 95 per cent glycerol at 0°C and pestle type homogenizers has been developed for isolating nuclei from Ehrlich ascites cells [ 141. The latter are very difficult to disrupt in pestle homogenizers when sucrose solutions are used. It thus seemed desirable to compare DNA isolated from Ehrlich ascites nuclei with that from the Ehrlich ascites whole cells. For further comparisons it appeared advantageous to isolate DN,4 from calf thymus tissue and nuclei. The unexpected results from such comparisons will be described along with other data in the discussion.