Showing papers by "David D. Sabatini published in 1975"

Direct association of messenger RNA with microsomal membranes in human diploid fibroblasts.

Abstract: Messenger RNA (mRNA) of membrane-bound polysomes in a membrane fraction of WI-38 cells remains associated with the microsomal membranes even after ribosomes and their nascent polypeptide chains are removed by using puromycin in a high salt buffer or by disassembling the ribosomes in a medium of high ionic strength lacking magnesium. mRNA either was specifically labeled in the presence of actinomycin D, or it was recognized by virtue of its affinity for oligo-dT. Poly A segments in bound mRNAs have an electrophoretic mobility in acrylamide gels which is characteristic of cytoplasmic mRNAs and corresponds to 150-200 adenyl residues. Extensive RNase treatment did not lead to release of the poly A segments of membrane-associated mRNA molecules either from an intact membrane fraction or from a membrane fraction previously stripped of ribosomes. On the other hand, RNase treatment led to the release and digestion of the nonpoly A segments of the mRNA molecules, indicating that the site of attachment of mRNA to the ER membranes is located near or at the 3' end of the molecule which contains the poly A. A direct association of mRNAs and endoplasmic reticulum membranes is considered in a modelto explain the assembly of bound polysomes and protein synthesis in a membrane-associated apparatus.

Structural and functional aspects of the protein synthesizing apparatus in the rough endoplasmic reticulum.

Abstract: The successful implementation of a genetic program requires that upon completion of translation polypeptides released from ribosomes are transferred to their final destination in the cell This appears to be a rather formidable process since, in a eukaryotic cell, the fate of a protein can be at least as diverse as the membranous structures within the cell and the subcellular compartments which they separate. For many proteins, these subcellular compartments serve only as the initial destination; transfer to another compartment or export from the cell may be their ultimate fate.