cDNA Selection with YACs

One of the major efforts in the field of positional cloning and the human genome project is to identify coding sequences or transcription units in large genomic regions such as yeast artificial chromosomes (YACs). The task proves to be challenging because only a small percent of the total DNA of the genome codes for mRNA, whereas the remainder consists of introns, intergenic sequences, and various repetitive sequences, Gene discovery by large scale genome sequencing with the available sequencing technology is not a practical approach, at least for the present. Several approaches for identifying expressed sequences have been described (1 –9 ). So far, however, experience with these methods at the megabase level remains limited.