Abstract
Membrane-bound ribosomes and messenger RNA remained associated with the microsomal membranes of human fibroblasts after cultures were treated with Verrucarin A, an inhibitor of initiation which led to extensive run-off of ribosomes from polysomal structures. When a membrane fraction from Verrucarin-treated cells containing such inactive ribosomes and mRNA was suspended in a medium of high salt concentration, extensive release of ribosomal subunits occurred without the need for puromycin. The mRNA nevertheless remained associated with the membranes. These results add support to the conclusion that, in human fibroblasts, mRNA is bound directly to ER membranes, independently of the ribosomes and nascent polypeptide chains.