Anatomy of Bovine Mammillitis DNA I. Restriction Endonuclease Maps of Four Populations of Molecules That Differ in the Relative Orientation of Their Long and Short Components

In this paper, we report that the DNA of bovine mammillitis virus (BMV) consists of two covalently linked components that are 71.5 x 10(6) and 15.7 x 10(6) in molecular weight and designated L and S, respectively. We further report that the BMV DNA consists of four equimolar populations differing only in the orientation of the L and S components relative to each other. This conclusion is based on the following: (i) The sum molecular weight of fragments generated by digestion of BMV DNA with Hsu I, Hpa I, Bgl II, or Xba I significantly exceeds the established molecular weight of the intact DNA. (ii) In each digest, the fragments form three groups differing in molar concentration. In reference to the molar concentration of intact DNA, each enzyme digest contained a set of four fragments 0.25 M in concentration, a set of four fragments 0.5 M in concentration, and a variable size set, unique for each enzyme digest, 1.0 M in concentration. (iii) Experiments involving digestion of intact DNA by lambda exonuclease followed by restriction endonuclease digestion established that each of four 0.5 M fragments were positioned at the termini of the BMV DNA. (iv) Complete maps for the fragments generated by each enzyme established that the 0.25 M fragments arise by fusion of the sequences of the terminal fragments when these are juxtaposed as a consequence of the inversion of L and S components. The maps also established the dimensions of the L and S components. We conclude that the structure of BMV DNA is similar to that of HSV DNA previously shown to consist of two unequal size components that invert relative to each other.