The vast majority of anogenital carcinomas are caused by high-risk human papillomaviruses (HPVs), and among Western nations HPV-16 is usually the most predominant cancer-associated type. As a DNA virus, HPV type 16 has a relatively stable genome that is believed to have co-evolved with its host over the millennia. Nevertheless, among the "wild" populations of HPV-16 that are circulating, a large number of variants have been identified, and these may have considerably different pathogenic

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... als. In this chapter, methods for screening and characterizing HPV-16 sequence variants are described. In particular, we describe methods for the identification of variation within the HPV-16 E5 open reading frame and for the detection of the nt 131 A→G mutation of the E6 ORF, using restriction fragment length polymorphism assays . In addition, we describe approaches for DNA sequencing and analysis. Such methods are likely to be of particular interest to those involved in epidemiological investigations of virus transmission and pathogenicity studies. branch occurs when trees are produced with a random input of the sequence files), and the drawing of phylogenetic trees. The trees can then be pasted into TreeView (http://taxonomy.zoology.gla.ac.uk/rod/treeview.html) in order to obtain phylogenetic trees that will indicate the amount of variation. Notes