Size of BACTERIAL cDNA Library?

the End jgraham at bronze.ucs.indiana.edu
Fri Oct 13 12:38:35 EST 1995


Does anyone have an idea of the relevant frequency and number of different
messages present in a "typical" bacterial cell growing in the laboratory?

In constructing a bacterial cDNA library, one needs to estimate the percentage 
of the total messages which are in a "low abundance" class and the number of 
different types of messages within that pool.

Sambrook et al. give estimates for a eukaryotic cell in terms of relatively 
"low abundance" messages constituting 30% of the total message pool, 
consisting of about 11,000 different sequences. In this case 11,000/0.3 or 
37,000 clones would be the minimum necessary cDNA library to contain all 
these sequences. Given the chances involved in obtaining all of them, a 
library about 3  to 4 times this size should be suficient for all but the
most "rare" RNAs to be present in a cDNA library.

Can anyone shed light on the case of a bacterial (E. coli?) cDNA library? 
Apparently there are apporximately 1800 identifiable spots on an 
O'Farrell 2-D protein gel, and the average bacterial mRNA encodes 3 proteins. 
This suggest a rough estimate of 600 different mRNAs.  Any notion of the 
number of these 600 which are "low abundance" messages? What portion of the 
total mRNA pool is made up of these less abundant messages? Thoughts on the 
applicablility of estimates for E. coli for other bacteria?

Thanks much, please E-mail me copies directly,

J. Graham
Biology Department
Washington University

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