MFP1, A NOVEL PLANT FILAMENT-LIKE PROTEIN WITH AFFINITY FOR MATRIX ATTACHMENT REGION DNA

The interaction of chromatin with the nuclear matrix via matrix attach ment regions (MARs) on the DNA is considered to be of fundamental impo rtance for higher order chromatin organization and regulation of gene expression. Here, we report a novel nuclear matrix-localized MAR DNA b inding protein, designated MAR binding filament-like protein 1 (MFP1), from tomato. In contrast to the few animal MAR DNA binding proteins t hus far identified, MFP1 contains a predicted N-terminal transmembrane domain and a long filament-like alpha-helical domain that is similar to diverse nuclear and cytoplasmic filament proteins from animals and yeast. DNA binding assays established that MFP1 can discriminate betwe en animal and plant MAR DNAs and non-MAR DNA fragments of similar size and AT content. Deletion mutants of MFP1 revealed a novel, discrete D NA binding domain near the C terminus of the protein. MFP1 is an in vi tro substrate for casein kinase II, a nuclear matrix-associated protei n kinase. Its structure, MAR DNA binding activity, and nuclear matrix localization suggest that MFP1 is likely to participate in nuclear arc hitecture by connecting chromatin with the nuclear matrix and potentia lly with the nuclear envelope.