NUCLEIC-ACID-BINDING PROPERTIES OF HNRNP-U SAF-A, A NUCLEAR-MATRIX PROTEIN WHICH BINDS DNA AND RNA IN-VIVO AND IN-VITRO/

We show that SAF-A, a nuclear protein which specifically binds vertebr ate scaffold-attachment-region (SAR) elements with high affinity is id entical with hnRNP-U, assumed to be involved in packaging of hnRNA in ribonucleoprotein particles. Ultraviolet cross-linking experiments sho w that the protein, referred to as hnRNP-U/SAF-A, is bound to chromoso mal DNA in vivo. In vitro, the isolated protein binds to double-strand ed and single-stranded DNA and forms higher ordered nucleic-acid-prote in complexes. Filter-binding experiments performed with different type s of natural and synthetic nucleic acids as substrates show that the p rotein binds DNA and RNA with different affinities and most likely at different binding sites. We conclude that hnRNP-U/SAF-A thus may have functions in the organisation of chromosomal DNA in addition to its su ggested role in hnRNA metabolism.