Three DNA repair genes, ERCC1, ERCC2, and by in situ hybridization using fluorescently-labeled cosmid probes. XRCC1 have been regionally mapped on human chromosome 19. ERCC1 and ERCC2 have been found to be separated by less than ERCC2 and XRCCl have been assigned to bands q13.2→q13.3 250 kb by large fragment restriction enzyme site mapping.

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DNA from a 50-kb yeast artificial chromosome (YAC) containing one human telomere was characterized. Cloned sequences from the centromeric end of this YAC (designated yRM2001) localized to several human chromosomes by somatic hybrid panel mapping. The telomeric end of the YAC contained both (TTAGGG)_n sequences and the previously characterized TelBam3.4 subterminal repeat element. A novel low-copy repeat element (designated HC1103) mapped 19 kb from the telomeric end of the YAC. This repeat was shown by fluorescence in situ hybridization to be present in several sub-telomeric regions (3q, 12p, 15q, 19p, and 20p) and at an interstitial site (2q13→q14) in all individuals studied, but to be polymorphically distributed at several other telomeres. The YAC vector-insert EcoRl cloning site was positioned 50 kb to 70 kb from chromosome termini in human genomic DNA using RecA-assisted restriction endonuclease (RARE) cleavage analysis. Our results suggest that the DNA segment cloned in yRM2001 contains a novel block of low-copy DNA consistently present at some human telomeres, but polymorphically distributed at others.

Expressed sequence tags [ESTs) from 298 clones have been generated from a randomly primed, normalized human adult thymus cDNA library. We describe the chromosomal localization of 136 of these ESTs by PCR-based mapping to a human monochromosomal somatic cell hybrid panel. Data base similarities to known genes are also described. A subset {n =18) of these randomly primed ESTs extended the sequence of ESTs from other tissues currently in dbEST. Of the nonrepetitive human adult thymus ESTs generated in this study, 237 (79.5%) have no similarity to current data base entries. This would suggest that our collection contains -100 new coding regions from thymus tissue, a large proportion of which likely will represent the middle regions of genes. The mapped ESTs should prove useful as new gene-based markers for mapping and candidate gene hunting, particularly when anchored to a well-developed physical map of the human genome.

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