Human herpesvirus 6B genome sequence: coding content and comparison with human herpesvirus 6A

Area of Science:

• Virology
• Genomics
• Molecular Biology

Background:

• Human herpesvirus 6 variants A and B (HHV-6A and HHV-6B) are closely related but exhibit distinct biological and epidemiological features.
• Previous studies indicated differences in T-cell infectivity, antibody reactivity, and disease associations.

Purpose of the Study:

• To report the complete genome sequence of HHV-6B strain Z29.
• To analyze the genetic content and compare the genomic sequences of HHV-6A and HHV-6B.
• To identify variant-specific genetic differences supporting their classification as distinct species.

Main Methods:

• Whole-genome sequencing of HHV-6B strain Z29.
• Bioinformatic analysis of genomic sequences, including identification of open reading frames (ORFs) and comparison of nucleotide and amino acid identities.
• Comparative analysis of divergent genomic regions, including direct repeats (DR) and the right end of the unique segment (U).

Main Results:

• The complete HHV-6B(Z29) genome is 162,114 bp, with a unique segment (U) and direct repeats (DR).
• 119 unique ORFs were predicted, with 9 ORFs specific to HHV-6B.
• Overall nucleotide sequence identity between HHV-6A and HHV-6B is 90%, with lower identity in DR (85%) and the right end of U (72%).
• Significant amino acid sequence divergence (>10%) was observed in 13 of 17 ORFs at the right end of U, excluding U94.

Conclusions:

• The comprehensive genome sequence of HHV-6B provides a detailed genetic map.
• Variant-specific genetic differences identified between HHV-6A and HHV-6B strongly support their designation as distinct herpesvirus species.
• Comparative genomics is crucial for understanding herpesvirus evolution and speciation.