Ordered mapping of FRA1H common fragile site, ADPRT and 5S rRNA genes at human chromosomal region 1q42.

In this work we have orderly mapped three markers localised in chromosome region 1q42: the human gene encoding poly(ADP-ribosyl) transferase (ADPRT or PARP), the main cluster of 5S rRNA genes and a DAPI-inducible common fragile site that cytologically corresponds to the 5-azacytidineinducible site FRA1H. ADPRT is a chromatin-associated protein that is thought to play an important role in several basic cellular processes including DNA replication and repair, recombination and maintenance of genomic integrity . The major 5S locus has been assigned to the chromosome region 1q42.1 and is constituted by approximately 150–180 repeats of the 5S unit. Common fragile sites on human chromosomes are particular regions that express gaps or breaks when the cells are exposed to specific chemical agents or conditions of culture. Some time ago, we identified in DAPI, a non-intercalating fluorochrome that binds preferentially to the AT bases of DNA, a compound capable of inducing the expression of a family of common fragile sites. DAPI has been added to human lymphocyte cultures to obtain metaphase spreads expressing the FRA1H common fragile site. Preparations have been simultaneously hybridized (FISH) with two DNA probes consisting of an ADPRT cDNA fragment and a 5S repeat unit. Our results show that the three markers analysed are localised at the region 1q42.1 in the following order: cen–FRA1H-ADPRT-5S–tel.