This helical domain is found at the N-terminal of plant E3-ligase proteins, including PP2CA INTERACTING RING FINGER PROTEIN 2 (PIR2, also known as MND1-interacting protein 1) and its paralogues RF4 and RF298 from Arabidopsis. The function of this domain is unknown. PIR2 is the closest homologue of PIR1 (PP2CA interacting RING finger protein 1) and both positively modulate ABA signaling by targeting PP2CA for degradation [1].

1: The RING finger E3 ligases PIR1 and PIR2 mediate PP2CA degradation to enhance abscisic acid response in Arabidopsis. Baek W, Lim CW, Luan S, Lee SC; Plant J. 2019;100:473-486. PMID:31436880