A cis-acting DNA regulatory element 3' to the A gamma-globin gene contains eight 
distinct regions of DNA-protein interaction distributed over 750 bp of DNA. The 
sequences of two foot-printed regions (sites I and IV) are A-T rich and generate 
a highly retarded complex on gel shift analysis with nuclear extract from human 
erythroleukemia (K562) cells. We have purified a 98-kD protein that reproduces 
this gel shift. Tryptic cleavage and peptide sequence analysis demonstrated that 
the 98-kD protein is identical to a recently cloned protein, special A-T-rich 
binding protein 1 (SATB1), that binds selectively to nuclear 
matrix/scaffold-associated regions of DNA (MARs/SARs). We have shown by 
functional analysis that the 3' A gamma regulatory element associates with the 
nuclear matrix. SATB1 mRNA was identified in K562 cells, and reverse 
transcriptase-polymerase chain reaction (RT-PCR) demonstrated its transcript in 
several other hematopoietic lines. Antisera to SATB1 caused ablation of the gel 
shift complex generated by both the crude nuclear extract and the purified 98-kD 
protein with the site I oligonucleotide. Furthermore, oligonucleotides that bind 
SATB1 inhibited formation of the site I gel shift complex when added as excess 
unlabeled competitor. An immunoblot analysis of the site I gel shift complex 
documented the presence of SATB1. Binding of SATB1 to two sites within the 3' A 
gamma regulatory element and its MAR/SAR activity suggests that this element may 
influence gene expression through interaction with the nuclear matrix.