Nucleic-acid-binding properties of hnRNP-U/SAF-A, a nuclear-matrix protein which binds DNA and RNA in vivo and in vitro


  • Note. The nucleotide sequence of MII is available under EMBL accession number L23999.

Correspondence to A. Richter, Department of Biology, University of Konstanz, Postfach 5560 (M614), D-78434 Konstanz, Germany
Phone:+49 7531 88 2125.
Fax:+49 7531 88 3688.


We show that SAF-A, a nuclear protein which specifically binds vertebrate scaffold-attachmentregion (SAR) elements with high affinity is identical with hnRNP-U, assumed to be involved in packaging of hnRNA in ribonucleoprotein particles. Ultraviolet cross-linking experiments show that the protein, referred to as hnRNP-U/SAF-A, is bound to chromosomal DNA in vivo. In vitro, the isolated protein binds to double-stranded and single-stranded DNA and forms higher ordered nucleic-acid–protein complexes. Filter-binding experiments performed with different types of natural and synthetic nucleic acids as substrates show that the protein 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 suggested role in hnRNA metabolism.