Exclusion of mRNPs and ribosomal particles from a thin zone beneath the nuclear envelope revealed upon inhibition of transport.
We have studied the nucleocytoplasmic transport of a specific messenger RNP (mRNP) particle, named Balbiani ring (BR) granule, and ribosomal RNP (rRNP) particles in the salivary glands of the dipteran Chironomus tentans. The passage of the RNPs through the nuclear pore complex (NPC) was inhibited with the nucleoporin-binding wheat germ agglutinin, and the effects were examined by electron microscopy. BR mRNPs bound to the nuclear basket increased in number, while BR mRNPs translocating through the central channel decreased, suggesting that the initiation of translocation proper had been inhibited. The rRNPs accumulated heavily in nucleoplasm, while no or very few rRNPs were recorded within nuclear baskets. Thus, the transport of rRNPs had been blocked prior to the entry into the baskets. Remarkably, the rRNPs had been excluded both from baskets and the space in between the baskets. We propose that normally basket fibrils move freely and repel RNPs from the exclusion zone unless the particles have affinity for and bind to nucleoporins within the baskets.
Department of Cell and Molecular Biology, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
Karin
K
Kylberg
Petra
P
Björk
Nathalie
N
Fomproix
Birgitta
B
Ivarsson
Lars
L
Wieslander
Bertil
B
Daneholt
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D002683:Chironomidae / Q000378:metabolism / Q000648:ultrastructure; D007814:Larva / Q000033:anatomy & histology / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism / Q000648:ultrastructure; D022022:Nuclear Pore / Q000378:metabolism / Q000648:ultrastructure; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D012469:Salivary Glands / Q000166:cytology
D021122:Protein Subunits; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein