[Polyribosomes loosely bound to endoplasmic reticulum membranes as an early step in the formation of a membrane-polyribosome complex].

Fractionation of polyribosomes tightly and loosely bound to the endoplasmic reticulum membranes in a sucrose density gradient was carried out. The obtained fractions (mono- and disomes, light and heavy polyribosomes) were analyzed in a homologous cell-free protein-synthesizing system in order to determine their total protein- and collagen-synthesizing activities. All the three fractions prepared by fractionation of the loosely bound polyribosomes were found to be actively involved in protein synthesis translation. In case of tightly bound polyribosomes only the fractions of light and heavy polyribosomes could actively synthesize the protein. Study of collagen synthesis in the given fractions revealed that in tightly bound polyribosomes this synthesis is localized in the light and have polyribosomal fractions, while in loosely bound ones only the fractions of mono- and disomes are responsible for active collagen synthesis. Based on the present-day concepts on the nature of bonds formed by interaction between the endoplasmic reticulum membranes and polyribosomes the polyribosomes loosely bound to the membranes cna be considered as an early step in the formation of a membrane-polyribosome complex.