Abstract: Methods and compounds are described that allow partitioning of messenger RNAs encoding runctionally related proteins, in particular those involved in cellular growth and differentiation, based upon binding to target sequences in the untranslated portions of the RNAS. The preparation of mRNA-subset libraries containing genes encoding such growth regulatory factors is described together with novel gene sequences derived useing these mRNA partitioning methods. These methods of mRNA partitioning allow access to growth regulatory factors unique to a given cell, tissue or tumor and provide a method of fingerprinting such factors.