THE ELEMENTARY RNP FIBER - NOT THE HIGHER-ORDER STRUCTURE - DETERMINES THE ALL-OR-NONE DISINTEGRATION BEHAVIOR OF BALBIANI RING PREMESSENGER RNP PARTICLES UPON RNASE-A TREATMENT

Balbiani ring premessenger ribonucleoprotein (RNP) particles are built from a 7-nm RNP fiber which is tightly folded into a ring-shaped RNP ribbon. Isolated particles are known to disintegrate in an all-or-none fashion upon RNase A treatment. In the present study we investigated whether this mode of disintegration is dependent on an intact particle structure or is inherent in the 7-nm fiber. When treated at low ionic strength, the Balbiani ring (BR) particles lost their higher order st ructure and the 7-nm fiber was unpacked, as evidenced by sucrose gradi ent sedimentation and electron microscopy. When treated with RNase A, unfolded as well as intact particles disintegrated in the all-or-none fashion, with similar kinetics and without apparent intermediates. Pro teinase K treatment, however, obliterated this pattern: the protein-fr ee particle RNA degraded progressively. As the typical disintegration pattern of the particles was not altered by unfolding, but was lost by deproteinization, the all-or-none mode of disintegration is likely to be a property of the 7-nm RNP fiber.