Nucleoplasmic beta-actin exists in a dynamic equilibrium between low-mobility polymeric species and rapidly diffusing populations.
Beta-actin, once thought to be an exclusively cytoplasmic protein, is now known to have important functions within the nucleus. Nuclear beta-actin associates with and functions in chromatin remodeling complexes, ribonucleic acid polymerase complexes, and at least some ribonucleoproteins. Proteins involved in regulating actin polymerization are also found in the interphase nucleus. We define the dynamic properties of nuclear actin molecules using fluorescence recovery after photobleaching. Our results indicate that actin and actin-containing complexes are reduced in their mobility through the nucleoplasm diffusing at approximately 0.5 microm2 s(-1). We also observed that approximately 20% of the total nuclear actin pool has properties of polymeric actin that turns over rapidly. This pool could be detected in endogenous nuclear actin by using fluorescent polymeric actin binding proteins and was sensitive to drugs that alter actin polymerization. Our results validate previous reports of polymeric forms of nuclear actin observed in fixed specimens and reveal that these polymeric forms are very dynamic.
Department of Oncology and 2Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 1Z2.
Darin
D
McDonald
Gustavo
G
Carrero
Christi
C
Andrin
Gerda
G
de Vries
Michael J
MJ
Hendzel
D000199:Actins / Q000032:analysis / Q000378:metabolism*; D001704:Biopolymers / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D004058:Diffusion; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D021381:Protein Transport / Q000502:physiology; D014158:Transcription, Genetic
D000199:Actins; D001704:Biopolymers; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins