RFX1, A TRANSACTIVATOR OF HEPATITIS-B VIRUS ENHANCER-I, BELONGS TO A NOVEL FAMILY OF HOMODIMERIC AND HETERODIMERIC DNA-BINDING PROTEINS

RFX1 is a transactivator of human hepatitis B virus enhancer I. We sho w here that RFX1 belongs to a previously unidentified family of DNA-bi nding proteins of which we have cloned three members, RFX1, RFX2, and RFX3, from humans and mice. Members of the RFX family constitute the n uclear complexes that have been referred to previously as enhancer fac tor C, EP, methylation-dependent DNA-binding protein, or rpL30 alpha. RFX proteins share five strongly conserved regions which include the t wo domains required for DNA binding and dimerization. They have very s imilar DNA-binding specificities and heterodimerize both in vitro and in vivo. mRNA levels for all three genes, particularly RFX2, are eleva ted in testis. In other cell lines and tissues, RFX mRNA levels are va riable, particularly for RFXZ and RFX3. RFX proteins share several nov el features, including new DNA-binding and dimerization motifs and a p eculiar dependence on methylated CpG dinucleotides at certain