The use of cDNA libraries has been central to many approaches in molecular biology. Prior to the development of functional genomics one of the primary starting points in molecular biology was to utilize some strategy to isolate a cDNA clone from a cDNA library that encoded the gene the individual researcher was interested in studying.
Many strategies are possible here.
We will return to look at these methods in more detail when we look at how individual genes are studied. Many of these same strategies can be used to isolate genomic clones as well. In addition, the representation of each sequence in the library should be determined by the abundance of its corresponding mRNA in the starting mRNA pool. This preparation can be used to infect E. coli and screened for the sequence of interest. As with phage libraries, plasmid libraries can be used directly or, most often, are amplified by allowing the bacteria containing the library to grow for a limited number of divisions.