D1 protein of Drosophila melanogaster. Purification and AT-DNA binding properties.

D1 protein of Drosophila melanogaster is a sequence-specific DNA-binding protein which recognizes AT-rich DNA sequences. AT-rich DNA sequences in eukaryotic organisms are distributed in two characteristic ways: flanking transcriptional units and in constitutive heterochromatin. D1 could play a role in regulation of gene expression and in geographical localization of DNA sequences within the nucleus. D1 has been partially purified by ion exchange chromatography. DNA-binding activity was investigated by nucleoprotein gel electrophoresis, using end-labeled restriction fragments varying in AT sequence content. D1 binds most tightly to the satellite sequence -AATAT-, with intermediate strength to the complex satellite (359-base pair repeat) and another AT-rich (68% AT) mixed sequence DNA, and least to the simple satellite sequence -AAGAG-.