TY - JOUR
T1 - The mechanism for producing two symmetries at the head-tail junction of bacteriophages
T2 - a hypothesis
AU - Serwer, Philip
N1 - Funding Information:
For comments on a preliminary draft of this manuscript, I thank Paul M. Horowitz and Neal C. Robinson. For secretarial assistance I thank Charlotte Farrell. Support was received from the National Institutes of Health (Grant AI 22568) and the Robert A. Welch Foundation (Grant AQ-764).
PY - 1987/7/21
Y1 - 1987/7/21
N2 - Some double-stranded DNA bacteriophages consist of DNA packaged in a proteinaceous capsid. The capsid has a DNA-enclosing outer shell (head) attached to an external projection (tail). At the head-tail junction is a ring of subunits (connector) that has either six or twelve-fold rotational symmetry, and is joined to the head at an axis of the head's five-fold rotational symmetry. The head is made of subunits in either an icosahedral array or an array consisting of two icosahedral hemispheres separated by a cylinder of subunits. During infection of a host, the head with connector is assembled as a procapsid that subsequently packages DNA and joins a tail. The mechanism for producing two symmetries at the head-tail junction has in the past been an unsolved problem. The observation that the connector of bacteriophage T7 does not nucleate asembly of the outer shell of T7's icosahedral procapsid (P. Serwer and R. H. Watson [1982] J. Virol. 42, 595-601) places a constraint on a solution for the above problem. To solve the above problem for icosahedral procapsids, it is proposed here that: (a) assembly of the outer shell of procapsids is nucleated by a six-membered ring of hexameric aggregates of the major outer shell protein, (b) the connector is assembled in the center of this ring, (c) one of the hexamers dissociates from the ring, creating a five-membered ring and forcing the connector to the inside of the outer shell. A related mechanism is proposed for nucleation of the elongated procapsid of bacteriophage T4.
AB - Some double-stranded DNA bacteriophages consist of DNA packaged in a proteinaceous capsid. The capsid has a DNA-enclosing outer shell (head) attached to an external projection (tail). At the head-tail junction is a ring of subunits (connector) that has either six or twelve-fold rotational symmetry, and is joined to the head at an axis of the head's five-fold rotational symmetry. The head is made of subunits in either an icosahedral array or an array consisting of two icosahedral hemispheres separated by a cylinder of subunits. During infection of a host, the head with connector is assembled as a procapsid that subsequently packages DNA and joins a tail. The mechanism for producing two symmetries at the head-tail junction has in the past been an unsolved problem. The observation that the connector of bacteriophage T7 does not nucleate asembly of the outer shell of T7's icosahedral procapsid (P. Serwer and R. H. Watson [1982] J. Virol. 42, 595-601) places a constraint on a solution for the above problem. To solve the above problem for icosahedral procapsids, it is proposed here that: (a) assembly of the outer shell of procapsids is nucleated by a six-membered ring of hexameric aggregates of the major outer shell protein, (b) the connector is assembled in the center of this ring, (c) one of the hexamers dissociates from the ring, creating a five-membered ring and forcing the connector to the inside of the outer shell. A related mechanism is proposed for nucleation of the elongated procapsid of bacteriophage T4.
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U2 - 10.1016/S0022-5193(87)80126-1
DO - 10.1016/S0022-5193(87)80126-1
M3 - Article
C2 - 3695545
AN - SCOPUS:0023661754
VL - 127
SP - 155
EP - 161
JO - Journal of Theoretical Biology
JF - Journal of Theoretical Biology
SN - 0022-5193
IS - 2
ER -