ARBP (attachment region binding protein) is an abundant nuclear protein that specifically binds to matrix/scaffold attachment regions (MARs/SARs). Here we show by gel filtration and gradient sedimentation that ARBP has an elongated shape. The sedimentation coefficient was determined as only 2.1 S. Furthermore, limited proteolysis of ARBP in situ (in isolated nuclei) with several proteases generated limiting resistant peptides from 14.5 to 18 kDa, that retained the ability to bind MARs specifically. This indicates that these peptides encompass the DNA binding domain of ARBP.
