The E1 ORF is one of the most conserved regions in the human papillomavirus (HPV) genome. The complete E1 gene of the HPV16 genome was amplified with four overlapping primer sets in 16 high-grade (CIN II, III) and 13 low-grade cervical (CIN I) intraepithelial neoplasias as well as in one cervical cancer case. Sequence analysis of the E6 and E7 genes was also carried out in the same cervical samples in order to confirm the association between nucleotide sequence variations in the HPV16 E1 ORF and HPV16 variant lineages. Analysis of the E1 ORF revealed 27 nucleotide changes, and these changes were correlated with those found in HPV16 Asian American and African type II variants. Of these nucleotide variations, A1668G, G2073A, T2169C, T2189C, A2453T, C2454T, A2587T and G2650A were identified only in high-grade dysplasia cases. A phylogenetic tree of the E1 ORF and nucleotide sequence analysis of the E1, E6 and E7 genes revealed that intratypic nucleotide sequence polymorphisms located in the E1 ORF can be used to identify the major phylogenetic branch to which a HPV16 genome belongs. Moreover, amplification of the E1 ORF revealed a disruption between nucleotides 878 and 1523 in five high- and two low-grade cervical cases, indicating that integration of HPV DNA occurs at an early stage of viral infection.

Recent studies have focused on sequence variation of the HPV16 E1 gene. The present study investigates the prevalence of E1-1374^63nt duplication in the Greek population, and the sequence variation at the 5' end of the E1 and E6 genes from samples that harbored this genetic alteration. Fifty HPV16 positive cervical samples, derived from Greek patients were investigated. The 5' end of the E1 gene was amplified through PCR and the variant amplicons were cloned, sequenced, and bioinformatically analyzed for selective pressure. The E1-1374^63nt duplication was identified in 24% of the examined samples, with the same prevalence in both high and low-grade cervical malignancies. The E1-1374^63nt duplication was linked to the European variant lineage (x²  = 5.076, P < 0.024) and it was significantly associated with the nucleotide variation A1053C (x²  = 23.102, P < 0.0001). Molecular evolution analyses anticipate that the E1-1374^63nt duplication induces functional constraints on the 5' end of E1 gene, and it is proposed that this duplication might not affect negatively the function or structure of the E1 protein. The E1-1374^63nt duplication is prevalent in the Greek population, whereas the A1053C variation might constitute a significant marker for the characterization of the E1-1374^63nt variant in the Greek population, thus providing significant information about viral pathogenicity.