~
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ti
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\ .. ~':~jFIGURE 102. Viral infection begins when ,Jiral DNA enters a bacterium. Bacterial DNA is
disrupted and viral DNA replicated. Synthesis of viral structural proteins and their assembly
into virus continues until the cell bursts, rl'leasmg particles. [From Hanawalt and Haynes, The
Chemical Basis of Life, p, 230,]A Molecular Trojan HorseWhat actually happens when the viral DNA enters a cell? The virus
"hopes", to speak anthropomorphically, that its DNA will get exactly the
same treatment as the DNA of the host cell. This would mean getting
transcribed and translated, th us allowing it to direct the synthesis of its own
special proteins, alien to the host cell, which will then begin to do their
thing. This amounts to secretly transporting alien proteins "in code" (viz.,
the Genetic Code) into the cell, and then "decoding" (viz., producing)
them. In a way this resembles the story of the Trojan horse, according to
which hundreds of soldiers were sneaked into Troy inside a harmless-
seeming giant wooden horse; but once inside the city, they broke loose and
captured it. The alien proteins, once they have been "decoded" (synthe-
sized) from their carrier DNA, now jump into action. The sequence of
actions directed by the T4 phage has been carefully studied, and is more or
less as follows (see also Figs. 102 and 103):
538Time elapsed
o min.
1 min.5 min.
8 min.Action taking place
Injection of viral DNA.
Breakdown of host DNA. Cessation of produc-
tion of native proteins and initiation of produc-
tion of alien (T 4) proteins. Among the earliest
produced proteins are those which direct the
replication of the alien (T4) DNA.
Replication of viral DNA begins.Initiation of production of structural proteins
which will form the "bodies" of new phages.Self-Ref and Self-Rep