IDENTIFICATION AND CHARACTERIZATION OF BC1 RNP PARTICLES

Rodent brain-specific small cytoplasmic BC1 RNA is an unusual RNA in s everal respects, It is an RNA polymerase III transcript expressed spec ifically in neurons, with regional and developmental regulation, Moreo ver, it is one of a few RNAs actively transported into dendrites, Thre e findings indicate that BC1 RNA exists as a ribonucleoprotein complex in vivo. First, the buoyant density of fractions containing BC1 RNA f rom brain extract on CsCl and Cs2SO4 gradients is 1.45 g/ml and 1.55 g /ml, respectively; this is consistent with the density of RNA-protein complexes, Second, in sucrose gradients, the BC1 particle has a larger S value (8.7S) than naked RNA (6.1S). Third, BC1 RNA from brain extra cts migrates with retarded mobility compared to naked BC1 RNA during a garose gel electrophoresis. Additionally, in comparison to the signal recognition particle (SRP), the BC1 RNP is more heat resistant and les s Mg2+-dependent. The buoyant density of the BC1 RNP suggests the pres ence of protein(s) with a total mass of about 138kD.