HUMAN GENES ENCODING U3 SNRNA ASSOCIATE WITH COILED BODIES IN INTERPHASE CELLS AND ARE CLUSTERED ON CHROMOSOME 17P11.2 IN A COMPLEX INVERTED REPEAT STRUCTURE

Coiled bodies (CBs) are nuclear organelles whose morphological structu re and molecular composition have been conserved from plants to animal s. Furthermore, CBs are often found to co-localize with specific DNA l oci in both mammalian somatic nuclei and amphibian oocytes, Much as rD NA sequences are called nucleolus organizers, we term these coiled bod y-associated sequences 'coiled body organizers' (CBORs). The only sequ ences that have been shown to be CBORs in human cells are the U1, U2 a nd histone gene loci, We wanted to determine whether other snRNA genes might also act as CBORs, In this paper we show that human U3 genes (t he RNU3 locus) preferentially associate with CBs in interphase cells. In addition, we have analyzed the genomic organization of the RNU3 loc us by constructing a BAC and P1 clone contig, We found that, unlike th e RNU1 and RNU2 loci, U3 genes are not tandemly repeated. Rather, U3 g enes are clustered on human chromosome 17p11.2, with evidence for larg e inverted duplications within the cluster, Thus all of the CBORs iden tified to date are composed of either tandemly repeated or tightly clu stered genes. The evolutionary and cell biological consequences of thi s type of organization are discussed.