I am grateful for the financial support of the predoctoral Traineeship given me by the U

We observe a very large temperature coefficient for the rupture rate, which arises from the effect of temperature on the viscosity of the DNA solution. When end effects can be neglected, the velocity is at a distance r from the center of the capillary. This energy is not recovered when the solution comes from the opposite end of the capillary.

In laminar flow, the shear gradient and residence time of a volume element of the fluid flowing through the capillary are a function of the radial position of that volume element. As indicated, the rate constant for rupture is expected to be a function of the gradient, G. The design of the capillary devices is such that not all of the fluid flows through the capillary on each pass (see Figure 1).

A full description of the procedure is given in the form of a recipe in Appendix B. A histogram of the resulting DNA as seen in the electron microscope is shown in Figure 2(a).

LENGTH OF MOLECULES

This treatment caused less than 1% of the linear substances to dissociate into half molecules (as estimated using Table II below). We know that about 12% of a typical DNA preparation has single-stranded breaks in the central quarter of the molecule. Note the good agreement between the points obtained from flow dichroism (0) and those obtained from band sedimentation (0).

The clue to the actual source of the temperature coefficient arose from the flow dichroism work of Callis and Davidson. Some conclusions derived in part from the viscosity data (see Discussion) suggested that the rupture rate per unit time may be a function of the residence time in the capillary. The shortest residence time occurs for the solution moving down the axis of the capillary.

The rate constant, k(G), can be written in terms of the displacement gradient or y using Eq. 23) derived in the experimental section. The last column of the table gives the fractional contribution of the second term of Eq. The extreme dependence of the fracture rate constant, k(G), on shear gradient (Eq. 44)) means that most fractures occur.

The circles are converted to linear in the first part of the experiment and can therefore affect the initial breaking rate. The number of molecules of each type can be written in terms of rate and time constants. In the range of shear gradients used for this work, the fracture rate is a continuous function of shear stress.

The figure shows a plot of the rate constant, k, versus the shear stress at the capillary wall, .,Pm. It is clear that the slope of the curve through the points, dk/d17Gm, is not constant. An insight into the real cause of the shear failure temperature coefficient arose from the work of Callis and Davidson.

That is, most of the molecules are in equilibrium between A and B as they fall through the capillary. It is the average distance from the origin to the sphere at the bottom of the raft in the absence of hydrodynamic flow. Here l/J(x, t) is the probability that the bottom of the raft will be between x and x + dx at time t.

The position of the dumbbell tip relative to its center of mass given by Eq.

Fig. 3. Typical band sedimentation profiles of A.hzb 5 c DNA in 3M CsCl. The direction of sedimentation is left to right

TIME

There are additional features of the dumbbell model that should be highlighted. 1) Our experiments show an inverse. In our formulation of the dumbbell model, we stipulated that when the dumbbell reached a certain critical extension, xc, it would break. However, it seems reasonable to use this value in view of the similarity of the solutions given by Eq.

The utility of the theoretical model just discussed was mainly to show how our experimental results with respect to capillary length turned out. The speed of this unfolding maneuver is limited by the speed at which segments of the DNA molecule can move through the solution and is therefore inversely proportional to the viscosity of the solution. A photoelectric control relay is activated whenever a meniscus comes between the light tubes of the corresponding tank.

The pH of the medium when mixed should be 7. 12) Good aeration is important during phage growth. Lift out the "cake" that forms at the interface between the two phases (or remove the upper and lower phases from it). It is useful to have only 4 ml of phage in each of the SW 50 rotor buckets.

In this work, the application of the half-molecule band method could give the distribution of breakpoint locations. But the DNA concentrations typically used in this work, both for breakage and rapid sedimentation, are low, and some of the more diluted components of the molecular weight distribution are lost in the noise of the centrifuge scanning system. Therefore, the method chosen here is electron microscopy, which can detect all components of the distribution.

The purpose of this appendix is to show that within the limits of the centrifuge detection system there is good agreement between the electron microscopy results and those obtained with the Vinograd-Bruner method. The concentration units were derived from the height of the DNA peaks as they appeared on scanner trace. 08 x 107 sec -2• With the experimental curve are two theoretical curves representing the contributions of the inhomogeneous centrifugal field and diffusion to the bandwidth.

The strand of DNA at the beginning of the string is in the shape of a lamella 0. The angle 0 is the angle between each segment and the line that runs from one end of the polymer to the other.