Transformation of a novel direct-repeat repressor element into a promoter and enhancer by multimerisation.

Studies on the regulation of interferon (IFN) responsive genes have mainly been centred on the highly conserved IFN stimulated responsive elements (ISREs) which can mediate type I and II IFN inducibility. To date little is known about other functional cis-acting regulatory motifs in IFN responsive genes. We report here on the identification of a repressor element in the human MxA gene defined to a 19 base pair (bp) region which houses a 9 bp direct repeat. DNA-specific protein binding on this element is not affected by IFN treatment and is distinct from ISRE binding proteins. Remarkably, contrary to expectations, when the repressor element is multimerised and spliced, in either orientation, to a reporter gene it behaves like a functional, constitutive promoter. Positioning the multimerised element in front of the SV40 enhancerless promoter also led to enhanced expression. The same protein(s) seem to bind to both the single repressor element and its multimerised form. This discovery of phenotypic reversal on a repressor element via multimerisation may have important implications in vivo.