Genome
HHV-6 has linear, double stranded DNA which contains an origin of replication, two 8–10 kb left and right direct repeat termini, and a unique segment that is 143-145kb. A variety of proteins are transcribed from the unique segment. Proteins are translated from mRNAs that are derived from transcripts of particular regions of the genome.
The origin of replication is where DNA replication begins. The origin of replication for HHV-6 is often labeled as "oriLyt" in the literature.
The direct repeat termini (labeled as DRL and DRR in the image) possess a repeated TTAGGG sequence, identical to that of human telomeres. Variability in the number of telomeric repeats is observed in the range of 15-180. These termini also contain the pac-1 and pac-2 cleavage and packing signals that are conserved among herpesviruses.
The unique segment contains seven major core gene blocks (U27-U37, U38-U40, U41-U46, U48-U53, U56-U57, U66EX2-U77, and U81-U82), which is also characteristic of herpesviruses. These conserved genes code for proteins that are involved in replication, cleavage, and packing of the viral genome into a mature virion. Additionally, they code for a number of immunomodulatory proteins. The unique segment also possesses a block of genes (U2-U19) that are conserved among HHV-6, HHV-7, and Cytomegaloviruses (the betaherpesviruses). Many of these genes belong to the HCMV US22 family.
Read more about this topic: Human Herpesvirus 6