Interactions of liver endoplasmic reticulum membranes and polysomesin vitro

Abstract

The interactions of various preparations of endoplasmic reticulum membranes and polysomes have been studied by means of a sandwich sucrose gradient that clearly isolates free ribosomes, smooth endoplasmic reticulum (S.E.R.) and rough endoplasmic reticulum (R.E.R.) from the microsomal fraction of rat liver homogenates. Reconstructed rough membranes separate well from the native R.E.R. but occupy the same position along the gradient as the S.E.R. and the rough membranes, stripped of their ribosomes by means of LiCl. Native R.E.R. and S.E.R. do not bind any added labeled polysomes at 0 degree C; previous treatment with LiCl does not modify the behavior of S.E.R. The presence of cell sap during the binding reaction does not increase polysome fixation by stripped-rough membranes but protects in some way the polysomes and preserves all their original functional capacity of amino acid incorporation into protein.

The binding of monoribosomes, oligoribosomes and polyribosomes to reticular membranes from rat liver

“…Studies of the control of the binding of ribosomes to membranes are important because of their possible relationship to the control of protein synthesis, particularly in regard to the mechanisms whereby newly biosynthesized proteins find their correct location within the cell. Investigations using direct methods for measuring the binding have provided evidence that both small and large ribosomal subunits, monoribosomes and polyribosomes re-attach to reticular membranes degranulated by LiCl (Scott-Burden & Hawtrey, 1971;Khawaja, 1971Khawaja, , 1977Schiaffonati et al, 1975;Scott-Burden, 1976), EDTA plus ribonuclease (Shires et al, 1975), citrate plus pyrophosphate (Rolleston, 1972;Ekren et al, 1973) and KCl plus puromycin (Rolleston, 1972;Borgese et al, 1974;Davis & Morris, 1976). Differences in the binding of 'template-depleted polyribosomes', prepared by cell-free protein synthesis and high-salt treatment, and ribosomal subunits, prepared by KCl plus puromycin treatment, have been reported (Shires et al, 1975).…”