Demonstration of a 7-nm RNP fiber as the basic structural element in a premessenger RNP particle.
Balbiani ring granules in Chironomus salivary glands represent premessenger ribonucleoprotein (RNP) particles, each containing a 35- to 40-kb message for a secretory polypeptide. Their gross structure can be described as an RNP ribbon bent into a toroid. We now demonstrate that an unfolded, thin RNP fiber is observed after low salt treatment of isolated Balbiani ring granules. Moreover, the thin RNP fiber, 7 nm in diameter, can be revealed as the main structural element in Balbiani ring granules studied in situ in 3-D with electron microscope tomography. It is proposed that the thin RNP fiber consists of a premessenger RNA molecule coiled around a filamentous core of polymeric proteins, which has functional implications for processes such as assembly of RNP, intranuclear degradation of RNA, and delivery of RNA through the nuclear pores.
Lönnroth
A
A
Department of Molecular Genetics, Medical Nobel Institute, Karolinska Institutet, Stockholm, Sweden.
Alexciev
K
K
Mehlin
H
H
Wurtz
T
T
Skoglund
U
U
Daneholt
B
B
D000818:Animals; D002683:Chironomidae; D008854:Microscopy, Electron; D009994:Osmolar Concentration; D011487:Protein Conformation; D012261:Ribonucleoproteins / Q000378:metabolism* / Q000648:ultrastructure; D012469:Salivary Glands / Q000378:metabolism
D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein