Two new members of the emerging KDWK family of combinatorial transcriptionmodulators bind as a heterodimer to flexibly spaced PuCGPy half-sites

Initially recognized as a HeLa factor essential for parvovirus DNA replicat ion, parvovirus initiation factor (PIF) is a site-specific DNA-binding comp lex consisting of p96 and p79 subunits, We have cloned and sequenced the hu man cDNAs encoding each subunit and characterized their products expressed from recombinant baculoviruses. The p96 and p79 polypeptides have 40% amino acid identity, focused particularly within a 94-residue region containing the sequence KDWK. This motif, first described for the Drosophila homeobox activator DEAF-1, identifies an emerging group of metazoan transcriptional modulators. During viral replication, PIF critically regulates the viral ni ckase, but in the host cell it probably modulates transcription, since each subunit is active in promoter activation assays and the complex binds to p reviously described regulatory elements in the tyrosine aminotransferase an d transferrin receptor promoters. Within its recognition site, PIF binds co ordinately to two copies of the tetranucleotide PuCGPy, which, remarkably, can be spaced from 1 to 15 nucleotides apart, a novel flexibility that we s uggest may be characteristic of the KDWK family. Such tetranucleotides are common in promoter regions, particularly in activating transcription factor /cyclic AMP response element-binding protein (ATF/CREB) and E-box motifs, s uggesting that PIF may modulate the transcription of many genes.