An intronic silencer of the mouse perforin gene.

We have previously shown that the perforin gene locus is comprised of eight DNase I hypersensitive sites (DHS). Seven (DHS I-DHS VII) of them were CTL-specific whereas one (DHS VIII) in the second intron was expressed in a wide range of cell types. DHS VIII was highly AT-rich (75%) and was comprised of multiple sets of high mobility group (HMG)-I/Y binding site, two potential Special AT-rich Binding protein (SATB-1)-binding sites, and a long stretch of CTAT repeats, indicating that DHS VIII may relate to nuclear matrix-associated region (MAR). When DHS VIII was inserted into the perforin promoter-driven luciferase gene, it silenced the reporter gene transcription in CTLL-R8 cells in an orientation- and distance-independent manner. Moreover, this silencing effect was also observed in other promoters in a variety of non-CTL cell lines, suggesting that DHS VIII exerted a global silencing effect. Deletion analysis and gel-shift assays indicated that the silencing effect was mediated by the CTAT repeats and its binding protein called CTAT repeats-binding protein (CRBP).