Techniques of study

Advances in molecular biology  have given rise to techniques that have superseded more traditional methods for  studying nucleic acids  such as  melting temperature (Tm)  and cesium chloride or sucrose gradient buoyant density analyses. In particular, nucleic acid sequencing has made the analysis of viral genomes simpler, more efficient, and rapid. Viral genomes from  most of the  families have  been totally  sequenced and  their genes identified, allowing the  prediction, and  in  many cases  characterization, of viral  gene products. Bioinformatic comparisons of virus genes with known sequences stored on computer databases have revealed fascinating similarities between viral and cellular genes that have been conserved during the co-evolution of viruses and their hosts. Virusgenes have been cloned into a variety of vectors and analyzed by a number of techniques (e.g. site-directed mutagenesis) to study their role during virus replication and host infection and immunity.

A common technique still used for studying DNA virus genomes is to digest those using restriction enzymes, which cut DNA into small fragments at specific nucleotide sequences. The fragments are separated according to size using agarose gel electrophoresis, and this allows a characteristic restriction enzyme map to be derived for each virus genome. Direct digestion of RNA genomes is not possible, but with the discovery of the viral enzyme reverse transcriptase, it is possible to make a DNA copy of an RNA genome; this complementary DNA (cDNA) can then be digested with restriction enzymes to provide a genome restriction map.