Nuclear actin is associated with a specific subset of hnRNP A/B-type proteins.
Pre-mRNP complexes were isolated from rat liver nuclei as 40S hnRNP particles, and actin-binding proteins were collected by DNase I affinity chromatography. The bound proteins were analyzed by 2D gel electrophoresis, and the following five hnRNP A/B-type proteins were identified by tandem mass spectrometry: DBP40/CBF-A (CArG binding factor A), a minor hnRNP A2 variant and three minor hnRNP A3 (mBx) variants. DBP40 was chosen for further analysis of the association of actin with the pre-mRNP complex. It was shown in vitro that purified actin binds to recombinant DBP40 suggesting that the interaction between actin and DBP40 is direct in the pre-mRNP particles. The association of actin with DBP40 was further explored in vivo. It was shown in a transfection study that DBP40 appears both in the nucleus and cytoplasm. Microinjection experiments revealed that DBP40 is exported from the nucleus to the cytoplasm. Finally, RNA-protein and protein-protein cross-linking experiments showed that DBP40 interacts with poly(A)(+) RNA as well as actin, both in the nucleus and cytoplasm. We propose that actin associated with DBP40, and perhaps with additional hnRNP A/B-type proteins, is transferred from nucleus to cytoplasm bound to mRNA.
Percipalle
Piergiorgio
P
Department of Cell and Molecular Biology, Karolinska Institutet, Box 285, SE-171 77 Stockholm, Sweden.
Jonsson
Andreas
A
Nashchekin
Dmitri
D
Karlsson
Christina
C
Bergman
Tomas
T
Guialis
Apostolia
A
Daneholt
Bertil
B
D000199:Actins / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D013058:Mass Spectrometry; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D012322:RNA Precursors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism*
D000199:Actins; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012322:RNA Precursors; D012333:RNA, Messenger; D012261:Ribonucleoproteins; C444244:hnRNP A-B related protein, cat; C439768:hnRNP A2