THE ORGANIZATION OF THE GAMMA-GLUTAMYL-TRANSFERASE GENES AND OTHER LOW COPY REPEATS IN HUMAN-CHROMOSOME 22Q11

A clone map consisting of YACs, cosmids, and fosmids has been construc ted covering low copy repeat regions of human chromosome 22q11. A comb ination of clone restriction digest analysis, single-copy landmark con tent analysis, HindIII-Sau3Al fingerprinting and sequencing of PCR pro ducts derived from clones was required to resolve the map in this regi on. Seven repeat-containing contigs were placed in 22q11, five contain ing gamma-glutamyl transferase (GGT) sequences described previously. I n one case, a single interval at the resolution of the YAC map was sho wn to contain at least three GGT sequences after higher resolution map ping. The sequence information was used to design 1 a rapid PCR/restri ction digest technique that distinguishes the GGT loci placed in the Y AC map. This approach has allowed us to resolve the previous cDNA and mapping information relating to GGT and link it to the physical map of 22q11.