The genome of naturally occurring Epstein-Barr virus contains either t
wo or three copies of a 29-bp tandem repeat sequence in the first intr
on of the BZLF gene. These genotypes differ markedly in their distribu
tion between blood and epithelial tissues, presumably because they hav
e adapted to separate life cycles in these sites. The genotype prevale
nt in the blood also appears to be better able to transform B lymphocy
tes.