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I have read that DNA(after recombination) is packaged in bacteriophages lambda only if it's between 40000 and 53000 bp long. This constraint can be used to ensure packaging of recombinant DNA.

I don't understand why shorter DNA can not be packaged.

Source : Lehninger Principles of Biochemistry

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Does the Lehninger explicitly state that it is not possible? –  Chris May 1 at 18:16
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These values relate specifically to lambda phage. –  Alan Boyd May 1 at 19:56
    
@Chris Yes. And as Alan Boyd states, this values are applicable only for bacteriophage lambda. (Edited my question) –  biogirl May 2 at 16:12

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up vote 2 down vote accepted

For lambda:

If the distance between the two cos sites is less than ~37 kb, the resulting phage particle will be unstable. When the DNA is inside the capsid, it exerts pressure on the capsid. Likewise the capsid exerts an inward force on the DNA. If there is not enough DNA inside the capsid, it will implode from the inward force of the capsid. If the distance between the two cos sites is too far (~52 kb), then the capsid will be filled before the second cos is reached. The tail cannot be added because the DNA hanging out of the capsid is in the way and no infectious phage particle is produced.

http://www.microinmuno.qb.fcen.uba.ar/03-Bacteriophage.pdf

In contrast filamentous phage like M13 have no upper size limit, but since they get longer with more DNA they become physically fragile.

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