| Coilin is widely known as the protein marker of the Cajal body (CB), a subnuclear domain important to the biogenesis of small nuclear ribonucleoproteins and telomerase, complexes that are crucial to pre-messenger RNA splicing and telomere maintenance, respectively. Despite recognition as the CB marker protein, coilin is primarily nucleoplasmic and the function of this fraction is not fully characterized. Extensive studies have explored the interaction between coilin and various other protein components of CBs and related subnuclear domains, however only a few have examined interactions between coilin and nucleic acid. Here we show that coilin binds double stranded DNA and has RNase activity in vitro. We utilized bacterially expressed coilin fragments to map the region(s) important for RNA binding and RNase activity in vitro. We also identified specific in vivo associations between coilin and ribosomal RNA (rRNA), U small nuclear RNA (snRNA) and human telomerase RNA (hTR), which are altered upon treatment with DNA damaging agents. CBs associate non-randomly with Ul and U2 gene loci, which produce the snRNA component of the respective snRNP. Using chromatin IP (ChIP), we provide evidence of coilin interaction with specific regions of U snRNA gene loci. The primary transcripts of U1 and U2 snRNAs undergo a processing event prior to incorporation in the snRNP. We show that coilin displays RNase activity towards the CU region of the U2 snRNA primary transcript in vitro. Additionally, we provide evidence of coilin involvement in the processing of hTR both in vitro and in vivo. Following coilin knockdown or overexpression, there are distinct changes in the levels of pre-processed U1 and U2 snRNA, as well as in hTR and rRNA. These findings present newly discovered characteristics of coilin involving nucleic acids, and suggest additional functions of the CB marker protein in the cell. |
