In plant, primary transcripts (pri-miRNAs) transcribed from miRNA genes by RNA 
polymerase II are first processed into stem-loop pre-miRNAs and further chopped 
into ∼21 nt long miRNAs by RNase III-like enzyme DCL1. SERRATE (SE) protein is 
an essential component for miRNA processing by assisting DCL1 for accurate 
cleavage. Here we report the crystal structure of Arabidopsis SE core (residues 
194-543) at 2.7 Å. SE core adopts the 'walking man-like' topology with 
N-terminal α helices, C-terminal non-canonical zinc-finger domain and novel 
Middle domain resembling the leading leg, the lagging leg and the body, 
respectively. Pull-down assay shows that SE core provides the platform for HYL1 
and DCL1 binding, whereas in vitro RNA binding and in vivo mutant rescue 
experiments suggest that the non-canonical zinc-finger domain coupled with 
C-terminal tail binds miRNA precursors. SE presumably works as a scaffold-like 
protein capable of binding both protein and RNA to guide the positioning of 
miRNA precursor toward DCL1 catalytic site within miRNA processing machinery in 
plant.