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Differentiation of radioactive DNA and RNA deposited on filter paper discs can be accomplished by a relatively simple procedure. RNA can be efficiently removed by incubating the dises, impaled on pins, with 0.2 ml of 0.5 n NaOH for 90 min at 37°C. DNA can be removed after NaOH hydrolysis by treating the discs with 5% TCA for 30 min at 90°C. A correction is necessary to determine the actual amounts of DNA and RNA in order to account for the loss of DNA (13.8%) during the NaOH hydrolysis procedure.

Sensitive assays of histidase activity were used to follow the production of this enzyme as directed by a gene newly introduced into cells of Bacillus subtilis by transformation. Histidase activity can be detected in histidase-negative recipient cells within 1 hr after the addition of deoxyribonucleic acid extracted from histidase-positive donors. Enzyme production continues for one to two additional hours and then ceases. Histidase production in the transformed cells is fully sensitive to catabolite repression. Catabolite repression is rapidly established after transformation of recipient cells that are resistant to this form of regulation.

Oligonucleotides, 3–17 nucleotides in length, were generated from mouse L cell DNA and their dialysis and solubility limits were determined under a variety of conditions. After dialysis for 24-h oligonucleotides more than 4 nucleotides in length were retained. Ethanol precipitates at least 10–20 % of all classes of oligonucleotides and 65 % of high molecular weight DNA under our conditions; oligonucleotides longer than 15–16 nucleotides are precipitated to about the same extent as high molecular weight DNA. HClO 4 and trichloroacetic acid are equally effective in precipitating oligonucleotides: 50 % precipitation occurs at 17 nucleotides for HClO 4 and 16 nucleotides for trichloroacetic acid. Acid precipitation of oligonucleotides adsorbed on glass or paper fiber filters is different from that observed with solutions. The efficiency of binding of oligonucleotides increases with increasing chain length: 50 % binding occurs at 5–6 bases with paper and 9–15 with glass. These numerical estimates are important with reference to some current techniques and results concerning DNA repair.

From the yeastCandida utilis a compound was isolated which uncouples the process of cell growth and division by accelerating the cell division without influencing outgrowth of cell mass when applied on another population of identical yeasts. This compound accelerated the initiation of DNA synthesis and had no influence on the synthesis of RNA and protein. Moreover, in the presence of division inducing factor the yeasts started multiplication before the content per cell reached the control level. The stimulating effect of division inducing factor was not obvious when the proteosynthesis of yeast cells was inhibited. We concluded that the division inducing factor regulates the formation of a protein which is synthesized in a very small amount and has a role in the initiation of DNA replication.

Polyoma virus particles were purified by equilibrium centrifugation in CsCl. Particles from three regions of the density gradient were examined for infectivity, for their ability to induce expanded pools of deoxyribonucleic acid (DNA) precursors, and for their ability to stimulate the synthesis of DNA. The most infectious population of particles, the virions, having a buoyant density of 1.33 g/ml, gave the greatest stimulation of the DNA-synthesizing apparatus of mouse embryo cells. Empty particles at density 1.29 g/ml had no DNA stimulatory activity. A population of particles of intermediate density, referred to as pseudovirions, was also much less active than virions in stimulating DNA synthesis, and the limited stimulatory activity of the latter fraction may be accounted for by its measured contamination with infective particles.