MadSci Network: Molecular Biology
Query:

Re: Follow-up question to Jani Raty

Date: Thu Nov 30 11:53:23 2000
Posted By: Jani Räty, Grad student, Biotechnology, University of Kuopio
Area of science: Molecular Biology
ID: 975548311.Mb
Message:


Sorry, the question and your goal were not clear to me in first question.
Question is relevant when you are trying to achieve genetic library, for 
example.

I can see two main reasons for E.coli having just one plasmid inside.

1) The consentration of bacteria, when transforming the cells. If you have 
high concentration of cells compared with plasmids in solution, the 
probability of just one plasmid entering the cell is high.

2) If all plasmids have the same resistance gene (Tetracycline etc), its 
not favourable to bacteria to have 2 copies of same resistance plasmid. The 
other one will be soon deleted. So a mutant, which has only one plasmid, 
will gain advantage when dividing, so it will more probably form 99,9% of 
the colony.

I hope this helps.
A good source for more information:
Watson J, Gilman M, Witkowski J and Zoller M: Recombinant DNA, 2nd edition

And  http://wine1.sb.fsu.edu/bch5425/lect27/lect27.htm http://www.protocol-online.net/molbio/DNA/dna_library.htm


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