Messenger ribonucleoproteins (informosomes) and RNA-binding proteins.

Messenger ribonucleoproteins, first discovered in 1964 in our laboratory as free mRNA-containing particles of fish embryo cytoplasm and designated as informosomes, proved to have a universal occurrence in eukaryotic cells. Messenger ribonucleoproteins of different intracellular localization such as free cytoplasmic non-translatable informosomes, translatable messenger ribonucleoproteins in polyribosomes and nuclear pre-mRNA-containing particles are characterized by a number of features common for all of them. However, the transport from the nucleus into the cytoplasm as well as the transition from the free non-translatable state into the polyribosome-bound translatable state are accompanied by essential changes in the protein moiety of the particles. The existence of free RNA-binding proteins in eukaryotic cells has also been shown. These proteins seem to represent a pool for the formation of messenger ribonucleoproteins (informosomes). It has recently been demonstrated that the eukaryotic translation factors and, in particular, both the elongation factors and some initiation factors are among the cytoplasmic RNA-binding proteins. It is suggested that the mRNA in eukaryotic cells at different stages of its life time carries on itself the proteins which are required for its own biogenesis, processing and transport (nuclear informosomes), for its existence in a temporarily inactive state (free cytoplasmic informosomes) and for its functioning as a template (polyribosomal informosomes): omnia mea mecum porto.