Capsid expansion follows the initiation of DNA packaging in bacteriophage T4 1 1 Edited by J. Karn

Capsid expansion follows the initiation of DNA packaging in bacteriophage T4 1 1 Edited by J. Karn Most bacteriophages undergo a dramatic expansion of their capsids during morphogenesis. In phages lambda, T3, T7 and P22, it has been shown that expansion occurs during the packaging of DNA into the capsid. The terminase-DNA complex docks with the portal vertex of an unexpanded prohead and begins packaging. After some of the DNA has entered, the major head protein undergoes a conformational change that increases both the volume and stability of the capsid. In phage T4, the link between packaging and expansion has not been established. We explored the possibility of such a connection using a pulse-chase protocol and high resolution sucrose gradient analysis of capsid intermediates isolated from wild-type T4-infected cells. We show that the first particle appearing after the pulse is an unexpanded prohead, which can be isolated in vitro as the ESP ( e mpty s mall p article). The next intermediate to appear is also unexpanded, but contains DNA. This new intermediate, the ISP ( i nitiated s mall p article), can also be isolated on agarose gels, permitting confirmation of both its expansion state and DNA content (∼10 kbp). It appears, therefore, that ⩾8% of the T4 genome enters the head shell prior to expansion. Following packaging of an undetermined amount of DNA, the capsid expands, producing the ILP ( i nitiated l arge p article), which is finally converted to a full head upon the completion of packaging. An expanded, empty prohead, the ELP ( e mpty l arge p article), was also observed during 37°C infections, but failed to mature to phage during the chase. Thus the ELP is unlikely to be an intermediate in normal head assembly. We conclude by suggesting that studies on assembly benefit from an emphasis on the processes involved, rather than on the structural intermediates which accumulate if these processes are interrupted. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Molecular Biology Elsevier

Capsid expansion follows the initiation of DNA packaging in bacteriophage T4 1 1 Edited by J. Karn

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Publisher
Elsevier
Copyright
Copyright © 1998 Academic Press
ISSN
0022-2836
DOI
10.1006/jmbi.1998.2179
Publisher site
See Article on Publisher Site

Abstract

Most bacteriophages undergo a dramatic expansion of their capsids during morphogenesis. In phages lambda, T3, T7 and P22, it has been shown that expansion occurs during the packaging of DNA into the capsid. The terminase-DNA complex docks with the portal vertex of an unexpanded prohead and begins packaging. After some of the DNA has entered, the major head protein undergoes a conformational change that increases both the volume and stability of the capsid. In phage T4, the link between packaging and expansion has not been established. We explored the possibility of such a connection using a pulse-chase protocol and high resolution sucrose gradient analysis of capsid intermediates isolated from wild-type T4-infected cells. We show that the first particle appearing after the pulse is an unexpanded prohead, which can be isolated in vitro as the ESP ( e mpty s mall p article). The next intermediate to appear is also unexpanded, but contains DNA. This new intermediate, the ISP ( i nitiated s mall p article), can also be isolated on agarose gels, permitting confirmation of both its expansion state and DNA content (∼10 kbp). It appears, therefore, that ⩾8% of the T4 genome enters the head shell prior to expansion. Following packaging of an undetermined amount of DNA, the capsid expands, producing the ILP ( i nitiated l arge p article), which is finally converted to a full head upon the completion of packaging. An expanded, empty prohead, the ELP ( e mpty l arge p article), was also observed during 37°C infections, but failed to mature to phage during the chase. Thus the ELP is unlikely to be an intermediate in normal head assembly. We conclude by suggesting that studies on assembly benefit from an emphasis on the processes involved, rather than on the structural intermediates which accumulate if these processes are interrupted.

Journal

Journal of Molecular BiologyElsevier

Published: Dec 4, 1998

References

  • Structural transitions during bacteriophage HK97 head assembly
    Duda, R.L.; Hempel, J.; Michel, H.; Shabanowitz, J.; Hunt, D.; Hendrix, R.W.
  • The largest (70 kDa) product of the bacteriophage T4 DNA terminase gene 17 binds to single-stranded DNA segments and digests them towards junctions with double-stranded DNA
    Franklin, J.L.; Haseltine, D.; Davenport, L.; Mosig, G.
  • The bacteriophage T4 DNA packaging apparatus targets the unexpanded prohead
    Jardine, P.J.; McCormick, M.C.; Lutze-Wallace, C.; Coombs, D.H.
  • Mutational analysis of the sequence-specific recombination box for amplification of gene 17 of bacteriophage T4
    Wu, C.H.; Black, L.W.

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