Molecular characterization of the purity of seven human chromosome-specific DNA libraries

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Abstract
We have characterized at the molecular level seven chromosome-specific libraries constructed in phage λ Charon 21A from flow-sorted human chromosomes. The purity of libraries prepared from chromosomes sorted from hamster × human cells was estimated by species-specific hybridization and ranged from 48% to 83% of clones containing human inserts. Among libraries of chromosomes from human cells, mass screenings were made for repetitive sequences and 20 clones from the # 18 and # 20 libraries were analyzed in detail. Ten to fifteen percent of all clones contain sequences which can be mapped; 80 100% of these derive from the intended chromosome of origin, demonstrating very high purity and a 35 × enrichment of chromosome-specific sequences over a total genomic library. The two libraries contain a high, though dissimilar, percent of repeat-containing clones; the # 18 library has 55% repetitive clones and the # 20 library 85%. This dissimilarity may be due to a difference in insert size distribution, since the # 18 library has smaller inserts than the # 20. This could be caused by variation in extent of digestion of insert DNA and/or differences in sequence organization between the two chromosomes. A method more sensitive than conventional plaque-lift screening was used to detect repetitive inserts; in this way nearly all repetitive clones could be eliminated before purification of their DNAs.