Isolation and characterization of four novel parsley proteins that interact with the transcriptional regulators CPRF1 and CPRF2

The common plant regulatory factors (CPRFs) from parsley are transcription factors with a basic-leucine-zipper motif that bind to cis-regulatory eleme nts frequently found in promoters of light-regulated genes. Proposed to fun ction in concert with members of other transcription factor families, CPRFs regulate the transcriptional activity of many target genes. Here, we repor t that, in contrast to CPRF2, which operates as a transcriptional activator , CPRF1 functions as repressor in vivo. Two-hybrid screens using CPRF1 and CPRF2 as "baits" resulted in the isolation of four novel parsley proteins w hich interact with either CPRF1 or CPRF2 in vivo. Three of these factors re present new parsley bZIP factors, designated CPRF5-CPR-F7, whereas the four th, named CPRF1-interacting protein (CIP), shows no homology to any other k nown protein. CPRF5 and CIP specifically interact with CPRF1, whilst CPRF6 and CPRF7 exclusively form heterodimers with CPRF2. CPRF5, CPRF6 and CPRF7 are transcription factors that exhibit sequence-specific DNA-binding as wel l as transactivation abilities, whereas the function of CIP remains elusive . The newly isolated CPRFs and CIP are constitutively localized in the nucl eus in parsley protoplasts. Furthermore, mRNA accumulation studies revealed that the expression of these novel bZIP genes and CIP is not altered by ex posure to light. We discuss the possible roles of the newly identified prot eins in CPRF1- and CPRF2-dependent target gene expression.