PBF-2 is a novel single-stranded DNA binding factor implicated in PR-10a gene activation in potato

Elicitor-induced activation of the potato pathogenesis-related gene PR-10a requires a 30-bp promoter sequence termed the ERE (elicitor response elemen t) that is bound by the nuclear factor PBF-2 (PR-10a binding factor 2). In this study, PBF-2 has been purified to near homogeneity from elicited tuber s through a combination of anion-exchange and DNA affinity chromatography. Evidence demonstrates that inactive PBF-2 is stored in the nuclei of fresh tubers and becomes available for binding to the ERE upon elicitation. A pro tein with an apparent molecular mass of 24 kD (p24) is a DNA binding compon ent of PBF-2. A cDNA encoding p24 has been cloned and encodes a novel prote in with a potential transcriptional activation domain that could also act a s a single-stranded DNA binding domain. Both PBF-2 and the cDNA-encoded pro tein bind with high affinity to the single-stranded form of the ERE in a se quence-specific manner. The inverted repeat sequence of the ERE, TGACAnnnnT GTCA, is critical for binding of this factor in vitro and for PR-10a expres sion in vivo, supporting the role of PBF-2 as a transcriptional regulator.