Exceptions

1
Exceptions

• The triangulation number is not always equal to
  the number of different subunit environments.
• e.g. Papovaviruses, T7, 6 subunit environments
  (360 subunits)
• Papillomaviruse (Belnap etal, Klug
  etal).
• For some multi-layer viruses, the T numbers of
  the different layers might be different.
• e.g. BTV, Touter13l, Tinner2
• RDV, Touter13l, Tinner1.
• Some viruses have unusual arrangement of the
  subunits.
• e.g. L-A virus, T1, 120 subunits which are
  arranged as 60 asymmetric dimers
• Bacteriophage F6, the core of which is a
  dodecahedron containing 120 subunits in a
  T2-like
• arrangement, i.e. on each facet
  there are 5 subunits.
• The big viruses with large T number are assembled
  utilizing the scaffolding and accessory proteins
  rather than the classical way of
  quasi-equivalence.
• e.g. HSV-1, T16, makes use of a scaffolding
  protein (VP22a) which organizes a procapsid
• Adenovirus, T25, assembles bricks
  (hexons) into complex structure by using a series
  of
• accessory proteins, polypeptide
  IX, polypeptide IIIa, and polypeptide VI.