Complex Bacterial Viruses with Double Stranded DNA

There is a large family of bacterial viruses that all have a complex form made up of a head, tail, and tail fibers (Fig. 17.13). The head of the virus particle contains a large molecule of linear dsDNA. They include bacteriophages T4, Lambda, P1 and Mu, which are all used in bacterial genetics (see Ch. 18) and molecular biology. The number of genes ranges from Mu with approximately 40 genes to T4 with nearly 200. T4 and its close relatives are some of the most complex types of virus known.

The head of the Mu virus particle is more or less spherical (i.e., it is a symmetrical icosahedron). However, the head of T4 is relatively elongated in order to accommodate the much greater amount of DNA. Attached to the head is a tail with tail fibers that act as landing legs. These viruses bind to bacterial cells by means of recognition proteins on the end of their tail fibers. After setting down like lunar landers, their tails contract and they inject their DNA like miniature hypodermic syringes.

bacteriophage M13 A small male-specific filamentous virus that contains circular single-stranded DNA and infects Escherichia coli male-specific phage Virus that only infects "male" bacteria, i.e., those bacteria carrying the F-plasmid

FIGURE 17.13 Bacteriophage with Heads and Tails

Complex bacterial viruses such as Mu and T4 have a head region that holds the dsDNA, a tail region that injects the DNA into the bacteria, and tail fibers that recognize specific proteins on the bacterial outer membrane and so facilitate attachment. The contractile sheath helps inject the DNA from the virus head into the inside of the bacterium.

FIGURE 17.13 Bacteriophage with Heads and Tails

Complex bacterial viruses such as Mu and T4 have a head region that holds the dsDNA, a tail region that injects the DNA into the bacteria, and tail fibers that recognize specific proteins on the bacterial outer membrane and so facilitate attachment. The contractile sheath helps inject the DNA from the virus head into the inside of the bacterium.

Herpesviruses can remain latent for long periods of time.

Poxviruses are the largest animal viruses.

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