Chapter 3 Physical and Chemical Characteristics of Lambda DNA

Abstract

The DNA extracted from a λ phage particle is a double-stranded linear molecule. As explained below, the best estimate at present for the molecular weight of the sodium salt of λ DNA is 30.8 ± 1.0 × 10⁶, corresponding to 46,500 nucleotide pairs.

In this chapter we discuss the following properties of the DNA molecules of lambdoid phages: (1) molecular weights; (2) hydrodynamic properties; (3) base composition and the related properties of buoyant density and denaturation temperature; (4) the nature of the cohesive ends, and the kinetics and equilibrium of the formation of hydrogen-bonded circles; (5) inhomogeneities in the distribution of nucleotides along the chain; and (6) physical studies of the genetic map, especially as studied by electron microscopy.

There is a good deal of pertinent and interesting science and history in the Nobel lecture by Hershey (1970).

MOLECULAR WEIGHT
The ratio of the molecular weights of two DNA molecules may be compared with reasonable precision. Absolute molecular weights are more difficult to measure accurately. We discuss them first.

Absolute Measurements
A great deal of effort has been devoted to absolute molecular weight measurements of DNAs from T7, T5, T2, and T4 bacteriophages. With one or two of these accurately known, a relative method could be used for measurements of λ and other DNAs. In our opinion, T2 and T4 DNAs are of limited use as standards because of complications associated with glucosylation, and because of special difficulties associated with the measurement of molecular weights of such large molecules. Results...