Improved method for cloning DNA complementary to minor mRNAs: preparation of a hybridization probe from purified mRNAs encoding intermediate filament proteins.

A procedure for the rapid fractionation of mRNA has been used to enrich mRNAs encoding a set of intermediate filament proteins in trophoblastoma cells. The procedure involves sucrose-gradient fractionation followed by high-resolution preparative gel electrophoresis. Part of the enriched mRNA preparation has been used to prepare a hybridization probe to screen a trophoblastoma cDNA library in Escherichia coli. A small proportion of the clones hybridized to the probe, and among these a specific clone was identified.