Characterizing Viral Genomes

Isolation of purified virions provides a primary source of viral genomes. Isolating viral genomes from purified virions is relatively simple. All that is necessary is a mild disruption of the capsid proteins, and the nucleic acid can be isolated by phenol extraction. A famous electron micrograph of a partially disrupted capsid of bacteriophage T4 with its DNA genome extruded is shown in Fig. 11.6.

An accurate determination of the viral genome's nature and molecular size is one of the first things that must be done when working with a newly isolated virus. Such information is important in establishing a basic idea of the virus's genetic complexity. This information, taken together with general characteristics of the virion (i.e., enveloped or not, icosahedral, helical, or complex shape), can be used to make a preliminary assignment of the relationship between

Penton base and penton associated protein

Penton base and penton associated protein

Hexon

(hexon associated proteins bind groups of hexon subunits)

Hexon

Hexon

(hexon associated proteins bind groups of hexon subunits)

Penton base Penton associated protein ■ Fiber

- Core protein

Hexon associated protein ■ Core protein Hexon associated protein • Protein specific for groups of nine hexons

Fig. 11.5 Electrophoretic fractionation of the capsid proteins isolated from purified adenovirus virions. This complex virion contains many different structural proteins that can be fractionated by denaturing gel electrophoresis. The different band intensities do not correlate with protein size. This result demonstrates that the structural proteins are not present in equimolar amounts.

the new virus and known virus families using criteria outlined in Chapter 5, Part II. Ultimately, of course, a full determination of nucleotide sequence of the viral genome will provide information as to the number and specific amino acid sequences of the proteins it encodes, as well as a precise measure of its degree of relatedness to other viruses.

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