CLUSTERED ORGANIZATION AND CONSERVATION OF THE XIPHOPHORUS-MACULATUS D-LOCUS, WHICH INCLUDES 2 DISTINCT GENE-SEQUENCES

Genomic organization and chromosomal localization of a previously unch aracterized D (Donor) locus in Xiphophorus and Poecilia species was in vestigated using fluorescence in situ hybridization (FISH) and Souther n blot analysis. Part of this region is thought to be involved in the recombination event leading to formation of the Xmrk oncogene and it h as recently been shown that this locus includes two different genes, o ne with high homology to a zinc finger protein of the Kruppel type, an d the other an unknown gene with high similarity to a Caenorhabditis e legans gene. FISH to Xiphophorus chromosomes revealed that these two u nrelated genes are closely linked and clustered at a unique chromosoma l site. Southern blot hybridization patterns suggest that these genes exist in the genome as multiple copies. Furthermore, similar genomic o rganization profiles seem to prevail among other related fish. In part icular, our FISH experiments reveal the existence of a conserved homol ogous chromosomal segment harboring the zinc finger protein sequence i n several poeciliid fish.