Purification of two isoforms of hnRNP-U and characterization of their nucleic acid binding activity.
The scaffold attachment factor A (SAF-A; Romig et al., 1992), a human nuclear protein which specifically binds vertebrate SAR (scaffold attached region) DNA, is identical with hnRNP-U (Kiledjian & Dreyfuss, 1992). In this paper, we report on the purification of two forms of this protein that can be chromatographically separated. We show that the purified proteins represent two isoforms, form 1 and form 2 hnRNP-U, which differ in their primary structure. Both isoforms bind to double- and single-stranded DNA and RNA. In addition, they form higher ordered nucleic acid/protein complexes and specifically bind and aggregate the human SAR element MII at physiological ionic strengths. Electron microscopic analysis shows that the isoforms differ from each other, as form 1 hnRNP-U aggregates into long unbranched filamentous protein/DNA complexes whereas form 2 hnRNP-U aggregates as spheres with an average diameter of 35 nm.
Fackelmayer
F O
FO
Department of Biology, University of Konstanz, FRG.
Richter
A
A
D000595:Amino Acid Sequence; D004247:DNA / Q000378:metabolism; D006367:HeLa Cells; D034722:Heterogeneous-Nuclear Ribonucleoprotein U; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D007525:Isoelectric Focusing; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010449:Peptide Mapping; D012261:Ribonucleoproteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
D034722:Heterogeneous-Nuclear Ribonucleoprotein U; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012261:Ribonucleoproteins; D004247:DNA