Genetic variability of hexon loops 1 and 2 between seven genome types of adenovirus serotype 7.

In order to understand the evolutionary relationships between different genome types of adenovirus serotype 7, the nucleotide sequences of the hexon loops 1 and 2 from seven genome types have been determined. Their amino acid sequences comprising 473 to 476 residues were consequently analysed. The pairwise comparison of the sequences from seven genome types revealed the existences of two genome type clusters (GTCs). GTC1 includes Ad7p and Ad7p1, and GTC2 contains Ad7b, Ad7c, Ad7d, Ad7g and Ad7h. The amino acid similarity was 98.3-99.8% within a cluster and 93.0-94.5% between two clusters. However, the average amino acid similarity among 16 different human adenovirus serotypes was only 65% with two exceptions, 92.7% between Ad4 and Ad16, and 86.8% between Ad3 and Ad7. Two variable regions were found in the loops 1 and 2. A deletion of nine nucleotides was detected in the variable region 1 of all members of GTC2. According to the alignment of nucleotide sequences, two short direct repeats were found at the deletion junctions, indicating that GTC2 may be derived from GTC1 by illegitimate recombination. In variable region 2, the substitution from 443Leu (Ad7b) to Gln (Ad7d) dramatically affected the hydropathic characters of this region. The region surrounding 443Leu (Ad7b) manifested hydrophobicity whereas the region surrounding Gln (Ad7d) manifested hydrophilicity.