A protein from human sperm nuclei that specifically binds to Alu DNA repeats has been purified. The specific DNA binding site of this protein within the Alu sequence has been mapped by methylation interference and electrophoretic mobility shift assays. This sperm Alu binding protein selectively protects Alu elements from methylation in vitro and may be responsible for the unmethylated state of Alu sequences in the male germ line resulting in a parent-specific differential inheritance of Alu methylation.
