DNA-binding protein that promotes DNA condensation into transcriptionally inactive heterochromatin in terminally differentiated avian blood cells. Promotes tight packing of nucleosomes into spherical clusters by binding to linker DNA and subsequent oligomerization. Acts as a cysteine protease inhibitor towards CTSL (cathepsin L1) and CTSV (cathepsin L2), but does not inhibit serine proteases. Homodimer and homooligomer. Interaction with DNA promotes oligomerization. Associated with chromatin. Detected in all major blood cell types. Highly expressed in granulocytes (at protein level). Belongs to the serpin family. Ov-serpin subfamily.