A LARGE DNA-BINDING NUCLEAR-PROTEIN WITH RNA RECOGNITION MOTIF AND SERINE ARGININE-RICH DOMAIN/

cDNA species encoding a large DNA-binding protein (NP220) of 1978 amin o acids was isolated from human cDNA libraries. Human NP220 binds to d ouble-stranded DNA fragments by recognizing clusters of cytidines. Imm unofluorescent microscopy with antiserum directed against NP220 reveal ed a punctate or ''speckled'' pattern and coiled body-like structures in the nucleoplasm of various human cell lines. These structures diffu sed in the cytoplasm during mitosis. Western blot analysis showed that NP220 is enriched in the lithium 3,5-diiodosalicylate insoluble fract ion of nuclei. The domain essential for DNA binding is localized in C- terminal half of NP220. Human NP220 shares three types of domains (MH1 , MH2, and MH3) with the acidic nuclear protein, matrin 3 (Belgrader, P., Dey, R., and Berezney, R. (1991) J. Biol. Chem. 266, 9893-9899). M H1 is a 48-amino acid sequence near the N terminus of both human NP220 and rat matrin 3. MH2 is a 75-amino acid sequence homologous to the R NA recognition motifs of heterogeneous nuclear RNP I and L. It is repe ated three times in NP220 and twice in matrin 3. MH3 is a 60-amino aci d sequence at the C terminus of both NP220 and matrin 3. NP220 has an arginine/serine rich domain commonly found in pre-mRNA splicing factor s. Close to the domain essential for DNA binding, there are nine repea ts of the sequence LVTVDEVIEEEDL. Thus, NP220 is a novel type of nucle oplasmic protein with multiple domains.