Editing Bacteriophage (section)

=== Virion assembly ===
In the case of the [[T4 phage]], the construction of new virus particles involves the assistance of helper proteins that act catalytically during phage [[morphogenesis]].<ref name="pmid4878023">{{cite journal | vauthors = Snustad DP | title = Dominance interactions in Escherichia coli cells mixedly infected with bacteriophage T4D wild-type and amber mutants and their possible implications as to type of gene-product function: catalytic vs. stoichiometric | journal = Virology | volume = 35 | issue = 4 | pages = 550–563 | date = August 1968 | pmid = 4878023 | doi = 10.1016/0042-6822(68)90285-7 }}</ref> The base plates are assembled first, with the tails being built upon them afterward. The head capsids, constructed separately, will spontaneously assemble with the tails. During assembly of the [[Escherichia virus T4|phage T4]] [[virus|virion]], the morphogenetic proteins encoded by the phage [[gene]]s interact with each other in a characteristic sequence. Maintaining an appropriate balance in the amounts of each of these proteins produced during viral infection appears to be critical for normal phage T4 [[morphogenesis]].<ref name="pmid4907266">{{cite journal | vauthors = Floor E | title = Interaction of morphogenetic genes of bacteriophage T4 | journal = Journal of Molecular Biology | volume = 47 | issue = 3 | pages = 293–306 | date = February 1970 | pmid = 4907266 | doi = 10.1016/0022-2836(70)90303-7 }}</ref> The DNA is packed efficiently within the heads.<ref>{{cite journal | vauthors = Petrov AS, Harvey SC | title = Packaging double-helical DNA into viral capsids: structures, forces, and energetics | journal = Biophysical Journal | volume = 95 | issue = 2 | pages = 497–502 | date = July 2008 | pmid = 18487310 | pmc = 2440449 | doi = 10.1529/biophysj.108.131797 | bibcode = 2008BpJ....95..497P }}</ref> The whole process takes about 15 minutes.

Early studies of bactioriophage T4 (1962–1964) provided an opportunity to gain understanding of  virtually all of the genes that are essential for growth of the bacteriophage under laboratory conditions.<ref>Edgar RS Conditional lethals: in Phage and the Origins of Molecular Biology (2007) Edited by John Cairns, Gunther S. Stent, and James D. Watson, Cold Spring Harbor Laboratory of Quantitative Biology, Cold Spring Harbor, Long Island, New York {{ISBN|978-0-87969-800-3}}</ref><ref name="pmid15514035">{{cite journal | vauthors = Edgar B | title = The genome of bacteriophage T4: an archeological dig | journal = Genetics | volume = 168 | issue = 2 | pages = 575–82 | date = October 2004 | doi = 10.1093/genetics/168.2.575 | pmid = 15514035 | pmc = 1448817 }}</ref>  These studies were made possible by the availability of two classes of [[lethal allele|conditional lethal mutants]].<ref name="EpsteinBolle1963">{{cite journal|vauthors = Epstein RH, Bolle A, Steinberg CM, Kellenberger E, Boy de la Tour E, Chevalley R, Edgar RS, Susman M, Denhardt GH, Lielausis A|title = Physiological Studies of Conditional Lethal Mutants of Bacteriophage T4D|journal = Cold Spring Harbor Symposia on Quantitative Biology|volume = 28|year = 1963|pages = 375–394|issn = 0091-7451|doi = 10.1101/SQB.1963.028.01.053}}</ref> One class of such mutants was referred to as [[stop codon|amber mutants]].<ref name="EpsteinBolle1963"/>  The other class of conditional lethal mutants was referred to as [[temperature-sensitive mutant]]s<ref name="pmid14156925">{{cite journal | vauthors = Edgar RS, Lielausis I | title = Temperature-sensitive mutants of bacteriophage T4D: Their isolation and Characterization.| journal = Genetics | volume = 49 | pages = 649–62 | date = April 1964 | issue = 4| doi = 10.1093/genetics/49.4.649| pmid = 14156925 | pmc = 1210603}}</ref>  Studies of these two classes of mutants led to considerable insight into  the functions and interactions of the proteins employed in the machinery of [[DNA replication]], [[DNA repair|repair]] and [[genetic recombination|recombination]], and on how viruses are assembled from protein and nucleic acid components (molecular [[morphogenesis]]).