In nucleoli, the steady state of nucleolar proteins is leptomycin B-sensitive.
BACKGROUND
The nucleolus is a dynamic structure. It has been demonstrated that nucleolar proteins rapidly associate with and dissociate from nucleolar components in continuous exchanges with the nucleoplasm using GFP (green fluorescent protein)-tagged proteins. However, how the exchanges within one nucleolus and between nucleoli within the nuclear volume occurred is still poorly understood.


RESULTS
The movement of PAGFP (photoactivatable GFP)-tagged proteins that become visible after photoactivation can be followed. In the present study, we establish the protocol allowing quantification of the traffic of PAGFP-tagged nucleolar proteins in nuclei containing two nucleoli. The traffic in the activated area, at the periphery of the activated area and to the neighbouring nucleolus is measured. Protein B23 is rapidly replaced in the activated area, and at the periphery of the activated area the steady state suggests intranucleolar recycling of B23; this recycling is LMB (leptomycin B)-sensitive. The pool of activated B23 is equally distributed in the volume of the two nucleoli within 2 min. The three-dimensional distribution of the proteins Nop52 and fibrillarin is less rapid than that of B23 but is also LMB-sensitive. In contrast, traffic of fibrillarin from the nucleoli to the CB (Cajal body) was not modified by LMB.


CONCLUSIONS
We propose that the steady state of nucleolar proteins in nucleoli depends on the affinity of the proteins for their partners and on intranucleolar recycling. This steady state can be impaired by LMB but not the uptake in the neighbouring nucleolus or the CB.
Laboratory Nuclei and Cell Cycle, Institut Jacques Monod, CNRS, Université Paris VI and Université Paris VII, 2 place Jussieu, 75251 Paris Cedex 05, France.
Eleonora
E
Muro
Thang Q
TQ
Hoang
Aude
A
Jobart-Malfait
Danièle
D
Hernandez-Verdun
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D012680:Sensitivity and Specificity; D013997:Time Factors
D005231:Fatty Acids, Unsaturated; D009687:Nuclear Proteins; D049452:Green Fluorescent Proteins; C038753:leptomycin B