The plant homeodomain (PHD) zinc finger domain has a C4HC3-type motif, and is widely distributed in eukaryotes, being found in many chromatin regulatory factors (1).PHD is thought to be involved in chromatin-mediated transcriptional regulation (2). The PHD finger motif is reminiscent of, but distinct from the C3HC4 type RING finger.

1. http://pfam.xfam.org/family/PF00628

2. Rein Aasland, Toby J. Gibson, A.Francis Stewart (1995). The PHD finger: Implications for chromatin-mediated transcriptional regulation. Trends in Biochemical Sciences., 20(2):56-59. PMID:77015622