Nucleotide and amino acid sequence variations in the L1 open reading frame of human papillomavirus type 6

Abstract

Human papillomavirus (HPV) type 6 induces benign tumors such as condyloma acuminata and laryngeal papilloma. The HPV-6 DNA has been thought to be a heterogeneous group of subtypes and variant-types. To examine sequence variations of the HPV-6 L1 ORF, we analyzed by single-strand conformation polymorphism (SSCP) and by DNA sequencing 21 specimens from condyloma acuminata and laryngeal papilloma that harbor HPV-6 DNA. PCR products of HPV-6 DNA were digested with 6 restriction enzymes yielding 8 fragments, which were then analyzed by SSCP. The resolution patterns showed that the L1 coding sequences were separated into three SSCP groups, I, II, and III, and two minor groups, (I) and (III). By sequencing the five representatives of each SSCP group and by comparing these sequences with those of HPV-6a [Hofmann et al., 1995] and HPV-6b [Schwarz et al., 1983], we identified base substitutions at 20 positions in the L1 coding region and an amino acid substitution in one case.

Intratype sequence variation among clinical isolates of the human papillomavirus type 6 L1 ORF: clustering of mutations and identification of a frequent amino acid sequence variant.

“…Specific silent nucleotide substitutions at eight fixed locations in the HPV-6 L1 ORF were observed in 76 % of isolates. These eight substitutions have been previously described in either HPV-6a (Hofmann et al, 1995) or HPV-6 isolates from India, Japan, Philippines and the United States (Icenogle et al, 1991 ;Suzuki et al, 1997). These results indicate that the prototype HPV-6b is not the predominant subtype W. Caparro!…”

“…Icenogle et al (1991) described several nucleotide changes within a 253 nt fragment of the L1 ORF from different geographical isolates of HPV-6, but reported no amino acid substitutions. Suzuki et al (1997) reported, in addition to several silent nucleotide substitutions, an Asn-to-Thr substitution in aa 55 of the L1 protein. However, it is not known whether this substitution affects the stability, yield and\or morphology of the resulting VLPs compared to those derived from the prototype HPV-6b L1 sequence.…”

“…Three of them (nt 6598, nt 6625 and nt 6661) have been described, after sequencing of a subfragment of the L1 ORF, in HPV-6 isolates from India, Philippines and the United States (Icenogle et al, 1991). All eight substitutions have been described previously only in some HPV-6 L1 isolates from Japan (Suzuki et al, 1997).…”

“…2). Moreover, all the substitutions described by Icenogle et al (1991) and 80 % (16\20) of those described by Suzuki et al (1997) in HPV-6 L1 isolates from India, the United States Philippines and Japan can be located within these three regions.…”