Figure 1
Overview of the types of herpesvirus genomes and the structure of virion. (I) The type A genomes (e.g., EHV-2) consist of a unique (U) region that is flanked by a direct terminal repeat (TR). The type B structure (e.g., Kaposi’s sarcoma-associated herpesvirus) also consists of a U region flanked by variable numbers of TRs. The type C genomes (e.g., Epstein-Barr virus) harbour variable numbers of terminal sequences and an internal direct repeat that is unrelated to the TR and splits the U region into two unique regions (UL and Us). The type D (e.g., PRV) and E (e.g., HSV-1) genomes contain UL and US regions that are each flanked by terminal and internal inverted repeats (TRL/IRL and IRS/TRS). The TRL/IRL regions are very short in some type D genomes (e.g., VZV), whereas they are longer in viruses with class E genomes. In the type E structure, there is also a terminal direct repeat of hundreds of base pairs that is known as the a sequence. Moreover, an inverted copy, known as the a’ sequence, is present internally. (II) The structure consists of four elements: (1) a core containing the viral dsDNA; (2) a T=16 icosahedral capsid encircling the core; (3) an amorphous protein layer called the tegument that surrounds the capsid; and (4) an outer lipid envelope (some inspiration came from these articles5, 6, 7, 9, 10)
