NFYi5 is an inhibitor of nuclear transcription factor-Y (NF-Y). It disrupts the binding of NF-Y to DNA, accelerates the ubiquitin-independent degradation of the NF-YA subunit, and reduces the transcriptional activity of NF-Y. As an antimitotic agent, NFYi5 decreases the mRNA levels of NF-Y target genes without affecting the expression of housekeeping genes, thereby inhibiting cell proliferation. NFYi5 is applicable in studies of tissue fibrosis.