The identification of cDNA clones that include the 3' end of mRNA

A method is presented that facilitates the identification of cDNA clones corresponding to the polyadenylated 3' end of mRNA. It is based on the use of a poly dT probe that is synthesized by homopolymer extension of commercially available oligo dT. The method is shown to work in Southern blot analysis of plasmid preparations and in situ with colonies.