The structure of nuclear ribonucleoprotein of amphibian oocytes.

Nuclear RNP from Triturus oocytes is organized as strings of beads which can be converted into 20-nm-diameter monoparticles with mild RNase treatment or into 5-nm-thick linear fibrils with low salt treatment. The protein component comprises a heterogeneous size-range of polypeptides which differ from the polypeptides of the other nucleoproteins of oocytes. The RNA is of high molecular weight, sediments mostly in excess of 50 S, and is capable of assuming considerable secondary structure. Duplex regions in the form of hairpin loops are present and may serve as focal points in the condensation of the RNP transcript fibres to generate the periodic beaded structure. The structure of the beads may be maintained by means of protein-protein interaction since at salt concentrations between 1 and 2 M NaC1 all of the proteins are released in a cooperative manner as various sized aggregates which sediment at 15-30 s. There are no specific proteins obviously peculiar to either the beaded or the fibrillar RNP configuration. The various properties of nuclear RNP are compared with those of chromatin.