The third to fifth zinc fingers play an essential role in the binding of ZFP809 to the MLV-derived PBS

Members of the kruppel-associated box-containing zinc finger protein (KRAB-ZFP) family mediate a number of cellular processes through binding to target DNA sequences via zinc fingers. Generally, zinc fingers recognize three-nucleotide sequences; however, this rule is not universally applicable. Zinc finger protein 809 (ZFP809) belongs to the KRAB-ZFP family and functions in repressing the expression of Moloney murine leukemia virus (MoMLV) via sequence-specific binding to the primer-binding site (PBS) located downstream of the MoMLV-long terminal repeat (LTR) and the induction of epigenetic modifications at LTR, such as repressive histone modifications and de novo DNA methylation. Previously, we demonstrated the role of the first to fifth zinc fingers of ZFP809 in binding to MLV PBS, indicating these zinc fingers do not recognize MLV PBS as a three-nucleotide sequence. Therefore, in the present study, we constructed truncated and mutated zinc fingers and examined their ability to bind to MLV PBS. The third to fifth zinc fingers of ZFP809 were found to be essential for binding to MLV PBS. Furthermore, the results of the present study indicate that other zinc fingers, which were not directly involved in binding to MLV PBS, may function in potentiating binding and stable protein expression. Further characterization of the amino acid sequences of zinc fingers will help further elucidate the functions and features of KRAB-ZFP and other zinc finger proteins.