A highly conserved nucleotide string shared by all genomes of human papillomaviruses

The nucleotide string TAAAACGAAAGT is the longest perfect homology shared by all sequenced human papillomavirus genomes. This nucleotide string, which was also found to be highly specific for human papillomavirus genomes, shares the same genomic position in all viral types (5' end of the E1 open reading frame) and putatively codes in every case for the same amino acids. One possible evolutionary model was used to estimate the probability of random occurrence of the nucleotide string in 10 human papillomavirus genomes. It assumed that the universal string had been subjected to the same mutation rate as the entire E1 open reading frame. The estimated probability was found to be very low, suggesting that the conservation of the string could not have resulted from random divergence and that its conservation among human papillomaviruses is likely to reflect the occurrence of biological constraints. It is speculated that this nucleotide string may be required to code for amino acids indispensable for the nuclear localization of E1-coded peptides or to bind cellular factors affecting viral replicative functions. Definitive evidence is expected to come from oligonucleotide-protein binding experiments and from site-directed mutagenesis of cloned HPV genomes. This motif, universal among human papillomaviruses, is being successfully used in the design of consensus primers from the early region.