High Effective Density Research Articles

The bouyant behavior of viral and bacterial DNA in alkaline CsCl.

In equilibrium gradient centrifugation, the banding polymer species is electrically neutral. The banding species for a negative polyelectrolyte with a polyanion P_(n)^(-z)n (where n is the degree of polymerization, and z the titration charge per monomer unit) in a CsCl salt gradient is CS_(zn)P_n. If the ion P_(n)^(-z)n is itself a weak acid, it may be titrated to the state P_(n)^(-(Zn+y)) by CsOH; the banding species is then Cs_(zn+y)P_n. Because of the large mass and high effective density of a Cs^+ ion, it is to be expected that the buoyant in a CsCl gradient of a polymer acid will be increased by such a partial alkaline titration with CsOH. This expectation has been confirmed for polyglutamic acid (where z = 0 at low pH). The guanine and thymine monomer units of DNA are weak acids. The present communication is concerned with the increase in buoyant of DNA in alkaline CsCl solutions. It is well known that the guanine and thymine protons are more readily titrated in denatured DNA than in native DNA. We find that the buoyant of denatured DNA and of single strand ϕX-174 DNA gradually increases as the pH of the solution is increased beyond pH 9.8. The of native DNA is not affected until a critical pH > 11 is reached, where the DNA abruptly denatures and increases in density. Similar increases in buoyant have been observed independently by Baldwin and Shooter in their studies of 5BU[overbar]-substituted DNA's in alkaline solutions.

A Design for an Electromagnet and Performance of a Small Model

The windings of the magnet are made of continuous lengths of copper tubing with cross section shown in Fig. 1. Water at high pressure is sent through the hollow center for cooling. The conductor is wound about the core in such a way that the resistance to the flow of the water is reduced to about half what would prevail in a magnet of conventional design. These features make possible a high effective current density. The disposition of the coils and the shape of the iron core were based on the experiences with the big magnets in Upsala and in Paris. A model gave the results indicated in Fig. 5. When the pole faces 2.5 cm in diameter were separated by 7 mm the field obtained was 33,200 gauss using 16 kw. The model was constructed to employ water at considerably higher pressures than were actually tried. A higher current density would then be permitted without risk of serious electrolytic corrosion.