Biology Reference
In-Depth Information
Fig. 4
Capsid assembly model. Shown here are interactions between the major capsid protein
(
MCP
, pUL85,
narrow trapezoids
), assembly protein precursor (pAP, pUL80.5
lines with empty
circles
), and protease precursor (pPR, pUL80a,
lines with filled circles
), and some of the putative
complexes they form (
1
). The largest represents a complete capsomer precursor (protocapsomer)
(
2
), but there is no direct evidence that its cytoplasmic assembly reaches completion. The minor
capsid protein (
mCP
, pUL85, 35 kDa,
light ovals
) and mCP-binding protein (
mCBP
, pUL46, 33
kDa,
darker oval
) also interact with each other in the cytoplasm to form heterotrimers, called tri-
plexes (
3
). The two types of oligomers are translocated into the nucleus (
4
) and coalesce to form
the procapsid (
Pro
), incorporating the portal-protein complex (pUL104, 78 kDa,
broken trapezoid
at bottom of capsid) (
5
). The terminase subunits are indicated by
shaded ellipses
below the portal
complex. Activation of pPR (
6
) results in cleavage and elimination of the internal scaffolding
proteins (pPR and pAP) from the capsid, before or during the process of DNA packaging (
7
).
Brackets around the B-capsid (
B
) indicate uncertainty about the nature of putative intermediate(s)
between procapsids and DNA-containing nucleocapsids. (Modified from Gibson 2006)
Fig. 3
(continued)
interaction of pAP and pPR with MCP; nuclear localization signals 1 and 2
(
NLS1
,
NLS2
); casein kinase II phosphorylation site (
black dots
between NLS1 and NLS2) of
undetermined significance; mitogen-activated protein kinase (
MAPK
) and glycogen synthase
kinase 3 (
GSK-3
) sites whose phosphorylation antagonizes pAP self-interaction (Casaday et al.
2004); and the five pPR self-cleavage sites: the maturational site (
M site
, VNA ¯S), which severs
the linkage of pPR and pAP to MCP; the release site (
R site
, YVKA ¯S), which separates the
proteolytic domain (assemblin) of pPR from the scaffolding portion (carboxyl end); the internal
site (
I site
, VEA ¯ A), which converts assemblin from an active single-chain form to a two-chain
form that retains activity, the cryptic site (
C site
, VDA ¯S) that interrupts the assemblin dimer
interface, and the tail site (
T site
, VLA ¯ A) detected upon refolding denatured pPR (Brignole and
Gibson 2007). Also shown is the amino acid sequence of the ACD and location of the critical
Leu47 (
red
; Leu382 in context of pPR sequence) within it. (Modified from Gibson 2006)
