Identification, cloning and sequence analysis of the equine adenovirus 1 hexon gene.

The research paper presents a study on the equine adenovirus 1 (EAdV1) hexon gene. The gene was identified through sequence homology with the human adenovirus 2, sequenced, and compared with other adenovirus proteins to identify key genomic features.

Cloning and Identification of the Hexon Gene

• The initial part of the study focuses on cloning and identification of the hexon gene of EAdV1. The gene was identified through its sequence similarity with the human adenovirus 2 (HAdV2).
• For this, HindIII restriction fragments containing the hexon and other viral genes were cloned into plasmids (pUC19 and pBlueScript SK(-)). Plasmids are circular DNA molecules used as vectors to insert DNA into a host cell.

Sequencing and Analysis of the Hexon Gene

• The hexon gene’s nucleotide sequence was determined completely, and partial sequences were obtained for seven other EAdV1 genes. The nucleotide sequence determination provides a detailed understanding of the gene’s structure and function.
• Amino acid sequence comparison with published adenovirus proteins helped researchers identify several viral genes, with the eight EAdV1 genes appearing to maintain the same relative order as homologous genes in other adenoviruses.

Property and Homology of the Hexon Gene

• The EAdV1 hexon protein was encoded between two other viral genes – the hexon-associated pVI upstream and the 23K proteinase gene downstream. The hexon protein comprised 2742 nucleotides, translating into 913 amino acids.
• Similar to other mastadenovirus genus members, the EAdV1 hexon featured two highly conserved genome segments at the N- and C-terminal ends. These ends flanked intermediate variable and hypervariable regions.
• Majority of residue differences between EAdV1 and other adenovirus hexons were found in two loops – known in other adenoviruses to protrude from the nucleocapsid surface.

Comparisons and Phylogenetic Analysis

• The study showed that the EAdV1 hexon protein showed the highest homology with the HAdV12 hexon, with 72% identical and 83% functionally similar residues. It also closely followed the bovine AdV3 hexon with 71% identities and 82% functional residue conservation.
• The study concludes with a phylogenetic analysis suggesting EAdV1 and other adenoviruses do not share an immediate common ancestor. This challenges the traditional belief that evolution proceeds through descent from a common ancestor.