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Figure 6.
Figure 6. The spinning connector model. (a) Schematic
arrangement of a portal vertex in projection view from the viral
prohead. A1 to A6 represent the ATPase (p16), S1 to S12
represent the connector subunits, and P1, 2, 3, etc. represent
the DNA phosphates of a DNA chain. For clarity, the model is
restricted to the description of one single DNA chain and one
lysine ring. The starting position (I) aligns a Lys (blue star)
of subunit S1 with the phosphate P1. Firing of the p16 ATPase
(A1) rotates the connector 12° clockwise while the DNA moves
linearly along the connector axis by 2 bp. A transient
interaction among the corresponding Lys from S2 and the
phosphates P2 (II) occurs at 6° rotation. The final stage
(III) is characterized by the interaction of Lys S3 and the
phosphate P3, which is accomplished after a further clockwise
rotation of the connector by 6°. This movement positions the
next p16 ATPase (A2) in an equivalent position with respect to
the DNA, to that of A1 in step I. (b) Schematic representation
of a side view of the model, corresponding to the same steps as
in (a). The lysine residues are depicted as blue spheres
labelled K1, K2,.... In step I there is a strong interaction
between lysine K1 and phosphate P1 (continuous line), while the
interaction of lysine K2 with phosphate P2 is still weak because
P2 is on a lower plane than the ring of lysine residues (broken
line). In step II the 6° rotation of the connector places
lysine K2 in an optimal position to interact with phosphate P2,
provided there is a longitudinal displacement of the DNA by 1
bp. In step III there has been a further 6° rotation of the
connector and another 1-bp displacement of the DNA, implying
that lysine K3 is now aligned with phosphate P3. The movement of
two base-pairs of DNA from I to III is, thus, correlated with a
rotation of the connector by 12°.
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