Structural characterization of the Molluscum contagiosum virus genome

The genome of Molluscum contagiosum virus (MCV) appears in an electron microscope as a linear, duplex DNA molecule having a mean contour length of 53.02 ± 1.87 μm. Vaccinia virus DNA, similarly processed and used for comparison, measures 53.03 ± 2.2 μm. The average molecular weight of MCV-DNA was calculated to be 118 × 10⁶. Single-stranded circles measuring twice the length of linear molecules were observed with both poxvirus DNAs following high levels of denaturation. However, partial denaturation profiles of MCV and vaccinia virus DNA differed markedly when mounted for microscopy under similar conditions. MCV-DNA consistently required an additional 10° equivalents to achieve comparable levels of denaturation. In contrast to vaccinia virus DNA, the most easily denaturable regions of the MCV genome appeared to be the ends of the molecule. When MCV-DNA was cleaved by restriction endonuclease BAM · HI, 12 fragments were produced ranging in size from 4 × 10⁵ to 31 × 10⁶ daltons as determined by agarose-gel electrophoresis and contour length measurements. Vaccinia virus DNA, similarly treated, produced more than 23 fragments which did not appear to correspond in size to those of MCV. With the aim of comparing the genetic and structural heterogeneity of the MCV genome, 11 independently isolated virus samples were analyzed by restriction endonuclease digestion and coelectrophoresis. Only three cleavage profiles were detected, with some fragments present in all three profiles, comigrating in agarose gels. We conclude, therefore, that the genome of Molluscum contagiosum virus is a continuous polynucleotide chain which is base paired to form a linear, duplex DNA molecule. Three genetic types of MCV were isolated from clinically typical skin lesions and identified in this study.