Biology Reference
In-Depth Information
Fig. 3.
Theoretical plot of % mutant the yield. Predictions were made with
Eq. (1), supposing that the total stoichiometry,
Z
, is equal to 12, and the
minimal number,
X
, of the bound mutant required to block the activity is 1
to 12, respectively.
Linear dsDNA viruses package their genome into a preformed
procapsid.
3,5,55
The packaging motor involves a dodecameric protein
connector
109-112
and two nonstructural components with certain char-
acteristics typical of ATPase.
113
In bacterial virus phi29, these two
nonstructural components are gp16 (a protein)
113,114
and pRNA.
115
Both of them have ATPase activity required for DNA encapsida-
tion,
113,116-118
and a small (120-base) viral RNA (pRNA) also plays an
essential role in the process.
115,119
Phylogenetic analyses of the virus-
encoded pRNAs
115,119
from other phages show similar secondary
structures.
120,121
Mg
++
induces a refolding of pRNA. This conforma-
tional change confers the pRNA to bind to the portal vertex (the site
on procapsids where DNA packaging occurs) of procapsids.
122
Approximately six pRNAs are attached to procapsids purified from
infected cells,
123
although the number required for DNA packaging is
unknown. The pRNA appears to leave the procapsid after DNA pack-
aging is completed (i.e. before tail assembly)
124
and accomplish the
DNA translocation process by their sequential action (Fig. 4).
125
pRNA contains two functional domains (Fig. 5). The procapsid
