The fractionation of pneumococcal genetic transforming activity

Abstract

1. 1. Pneumococcal DNA having transforming activities for resistance to streptomycin, aminopterin, canavanine, micrococcin and sulfonamides was chromatographed on columns of a polycarboxylate resin (IRC-50) and columns of methylated albumin-kieselguhr. Material determining the last three properties was eluted at constant proportion with DNA, whereas activities for the first two predominated in the earlier fractions. Transforming activity for the genetically linked pair, streptomycin-sulfonamide resistances, was distributed about a position intermediate between the peak positions of the single markers. 2. 2. The pneumococcal DNA is fractionated on IRC-50 according to both base composition and sedimentation coefficient. However, the various single genetic activities did not differ demonstrably in sedimentation coefficients as indicated by their distributions after sedimentation through sucrose gradients. 3. 3. A comparison of chromatographic behavior, temperature of critical heat inactivation and buoyant density in CsCl was made for several genetic markers. The ranking of transforming agents as to inferred guanine-cytosine contents was similar when based upon chromatographic behavior and buoyant density but different from that deduced from heat inactivation. On the basis of the first two properties, those molecules responsible for aminopterin and streptomycin resistance are the richest in guanine and cytosine, those transmitting sulfonamide, canavanine and micrococcin resistances are poorer in this regard. On the basis of heat inactivation, aminopterin resistance activity fulfils this expectation; however, streptomycin sulfonamide and canavanine resistances appear to be intermediate in guanine-cytosine, while micrococcin resistance appears to be lowest of all. 4. 4. Shear degradation of DNA results in a drop of several degrees in the temperature of critical heat inactivation of the agent for aminopterin resistance. Concomitant with this change, this agent drops in buoyant density and becomes the last activity to be eluted from columns. 5. 5. It appears that chromatographic behavior, buoyant density, and temperature of critical heat inactivation respond to different aspects of the same feature of DNA composition, presumably the guanine-cytosine content. It seems possible thate the heat inactivation may be dependent upon the base composition in a specific region of the particular DNA molecules involved, whereas the cromatographic behavior and buoyant density reflect the average base composition of the entire molecule.