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yowahoshi

Phage DNA

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Could you elaborate a little bit? Where have you heard/read this?

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Posted (edited)

Hi, i was reading  T.A Brown for recombinant DNA tech. so it is in chapter 2nd i.e VECTORS FOR GENE CLONING  under the subheading of THE PHAGE INFECTION CYCLE .

i am sharing the paragraph and  - With some phage types the entire infection cycle is completed very quickly, possibly
in less than 20 minutes. This type of rapid infection is called a lytic cycle, as release of the new phage particles is associated with lysis of the bacterial cell. The characteristic
feature of a lytic infection cycle is that phage DNA replication is immediately followed by synthesis of capsid proteins, and the phage DNA molecule is never maintained in a
stable condition in the host cell.

Edited by yowahoshi

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I started explaining about viruses before I realised that phages specifically only talk about bacteriophages. I kept the information as you may find it useful or interesting anyway.

The answer to your question, I would guess, is that it not great to do so for the phages. CRISPR systems may be one reason. Eukaryotic viruses (see below) can safely store their DNA within the nucleus, but this may be not feasible in bacteria. Instead even during latent periods they may only store their DNA within capsids. Sorry, I am not very familiar with phages;/ But based on this wikipedia article, I would guess that at least some viruses can stably integrate their DNA: https://en.wikipedia.org/wiki/Lysogenic_cycle 

This is in contrast to virus (please note I do not know enough about phages to say they do or don't have similar mechanisms) which don't immediately lyse their host cells. There are viruses which have a quiet phase, where they copy their RNA into DNA and store it close to the chromosomes within the nucleus. I am not very sure about the details/different types of latency, but some viruses can stay latent for super long periods of time. I think others can inhibit lysis for some time, thereby leading to larger amounts of viral particles. I am not sure if those that delay lysis (but do not become fully latent) also maintain viruses DNA as a stable molecule within the cell. I presume so, based on retroviruses existing, which insert copies into the chromosomal DNA of their host. https://en.wikipedia.org/wiki/Retrovirus 

Retroviruses such as HIV can also become fully latent, but recently I watched a video about Herpes virus (non retroviral) and how it escapes detection during latency: 

 

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OK, let's take a step back here a bit.

Phage roughly speaking have two states. One is the lysogenic cycle, the other one is the lytic one. If lysogenic they remain inactive and are stably reproduced with the host genome. Once certain conditions are met, e.g. if the bacterium is exposed to stress, the phage can enter the lytic cycle, in which it reproduces and eventually destroys its host.

Phages that have a lysogenic cycle are called temperate bacteriophages.

In contrast, there are also agressive phages that predominantly (or solely) use a lytic cycle for reproduction. These are, unsurprisingly, called lytic phages and this is what the text refers to.

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