Construction of an equalized cDNA library from human brain by semi-solid self-hybridization system.

A cDNA library enriched in clones for mRNA species (an equalized cDNA library) was constructed from human brain employing semi-solid self-hybridization system and cDNA amplification by in vitro transcription. Sequence analysis of the clones in the cDNA library indicated that (1) clones representing abundant species such as those of mitochondrial origin and expression sequence taq (EST) are drastically reduced in their proportion compared to the original library and (2) clones representing rare mRNA species or which do not have matched sequences in the database increased substantially in their proportion. cDNA libraries thus constructed, therefore, are a good source for cloning of cDNA for rare mRNA species from specific mammalian tissues and also for direct expression cloning since the inserts maintained their original molecular sizes after equalization.