Ribonucleoprotein properties

Mechanistic studies of RNA enzymes (ribozymes) and ribonucleoprotein (RNP) complexes such as the ribosome and telomerase, often seek to characterize RNA structural features, either dynamic or static, and relate these properties to specific catalytic functions. Many experimental techniques that probe RNA structure-function relationships rely upon site-specific incorporation of chemically modified ribonucleotides into the RNA of interest, often in the form of chemical cross-linkers to probe for sites of protein-RNA interaction or small organic fluorophores to measure dynamic structural properties of RNAs. The ability to arbitrarily modify any RNA molecule has been greatly enabled by modern RNA synthesis techniques however, there remains a practical size... 

In 1964 Spirin et al. discovered in embryonic cells cytoplasmic ribonucleoprotein particles containing rapidly labeled RNA with many properties of mRNA. The particles contain RNA and protein in a ratio of about 1 3 or 1 4. These particles, which are free cytoplasmic mRNA-protein complexes not combined with ribosomes, were named informosomes. Under ultracentrifugation they form a number of discrete peaks with sedimentation coefficients equal to 20, 30, 40, 50, 55, 65, and 75S (Spirin et al., 1964). 

This process has not yet been studied at all, and the mechanism of the movement of macromolecules from chromosomes to the cytoplasm is quite unclear. The only useful information is based on electron microscopic observations. One can observe particles presumably containing D-RNA, such as Beerman granules or perichromatin granules, interchromatin granules, and helices in different parts of the nucleus. They may be bound to chromatin threads or lie freely in the nuclear sap or even be in contact with the nuclear membrane. These pictures may reflect the movement of the particles from chromatin to the nuclear membrane (Beerman and Bahr, 1954 Stevens and Swift, 1966, Monneron and Bernhard, 1969). As all these types of particles are of ribonucleoprotein nature and have many properties similar to those of isolated nuclear D-RNP, it is possible to suggest that D-RNA moves to the nuclear membrane in a complex with informofers. 

Recently, we have demonstrated the existence of a poly(ADPR) polymerase activity associated with cytoplasmic free messenger ribonucleoprotein particles (mRNP) isolated from mouse plasmacytoma cells [4]. The enzyme does not require DNA for activity and is able to produce an ADP-ribosylation of some of the mRNP proteins. We have extended our observations to Krebs II ascites-tumor cells and to rat liver. In the present report, we will discuss some properties of this enzyme, particularly the activation by RNase A. 

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