COMPLEX BETA-SATELLITE REPEAT STRUCTURES AND THE EXPANSION OF THE ZINC-FINGER GENE-CLUSTER IN 19P12

We investigated the organization, architecture, and evolution of the l argest cluster (similar to 4 Mb) of Kruppel-associated box zinc finger (KRAB-ZNF) genes located in cytogenetic band interval 19p12, A highly integrated physical map (similar to 700 kb) of overlapping cosmid and BAC clones was developed between genetic STS markers D19S454 and D19S 269. Using ZNF91 exon-specific probes to interrogate a detailed EcoRI restriction map of the region, ZNF genes were found to be distributed in a head-to-tail fashion throughout the region with an average densit y of one ZNF duplicon every 150-180 kb of genomic distance. Sequence a nalysis of 208,967 bp of this region indicated the presence of two put ative ZNF genes: one consisting of a novel member of this gene family (ZNF208) expressed ubiquitously in all tissues examined and the other representing a nonprocessed pseudogene (ZNF209), located 450 kb proxim al to ZNF208. Large blocks of (similar to 25-kb) inverted beta-satelli te repeats with a remarkably symmetrical higher order repeat structure were found to bracket the functional ZNF gene. Hybridization analysis using the beta-satellite repeat as a probe indicates that p-satellite interspersion between ZNF gene cassettes is a general property for 1. 5 Mb of the ZNF gene cluster in 19p12. Both molecular clock data as we ll as a retroposon-mapping molecular fossil approach indicate that thi s ZNF cluster arose early during primate evolution (similar to 50 mill ion years ago). We propose an evolutionary model in which heteromorphi c pericentromeric repeat structures such as the beta satellites have b een coopted to accommodate rapid expansion of a large gene family over a short period of evolutionary time.