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G Brawerman

Publications and source records attributed to G Brawerman.

At least 55 records · Page 3Linked to original sources
PubMed1974

Elongation of the polyadenylate segment of messenger RNA in the cytoplasm of mammalian cells.

Chinese hamster and mouse sarcoma 180 ascites cells, treated with high levels of actinomycin D, still carry out limited poly(A) synthesis. The residual activity, which consists of poly(A) chain extension in the cytoplasm as well as in the nucleus, is essentially insensitive to cordycepin. Nuclear polyadenylation proceeds linearly and involves the gradual extension of unusually long poly(A) sequences. Cytoplasmic poly(A) labeling is initially more rapid than in the nucleus, but levels off within 5-10 min. It consists of addition of seven to eight AMP residues to the poly(A) sequences in preexisting mRNA molecules. The levelling off can be accounted for by a rapid turnover of the extremity of the poly(A) chain in the mRNA. Cytoplasmic poly(A) chain extension can be detected in cells not subjected to the actinomycin treatment. The rate of this process is of the same order of magnitude as that of new poly(A) transfer from nucleus to cytoplasm. It could serve to control the length of the poly(A) sequence in mRNA.

Adenine Nucleotides↗
PubMed1972

A particle associated with the polyadenylate segment in mammalian messenger RNA.

A structure consisting of poly(A) complexed with other components is released from polysomes by ribonuclease treatment. The poly(A) complex has a sedimentation value of 12-15, while the corresponding sedimentation value for free poly(A) is 4. The complex does not appear to represent an artifact formed by interaction of free poly(A) with either cytoplasmic or polysomal proteins. The polynucleotide released from the complex by treatment with sodium dodecyl sulfate shows the same electrophoretic mobility as that of poly(A) isolated from deproteinized polysomal RNA. The poly(A) in the complex is partially protected from digestion by T(2) ribonuclease. At least part of the poly(A) is available for base pairing with poly(U). The components associated with the poly(A) cause it to bind to Millipore filters at low ionic strength. These components are removed from the complex by Pronase digestion. The findings indicate that the poly(A) segment in messenger RNA serves as a binding site for a particle. This particle appears to consist of proteins.

Animals↗
PubMed1971

A polynucleotide segment rich in adenylic acid in the rapidly-labeled polyribosomal RNA component of mouse sarcoma 180 ascites cells.

The rapidly-labeled polyribosomal RNA component from mouse sarcoma 180 cells is retained on nitrocellulose (Millipore) membrane-filters at high ionic strength. This property is due to the presence of a polynucleotide sequence rich in adenylic acid that resists both T(1) and pancreatic RNase digestion. The resistant material shows sedimentation characteristics close to those of transfer RNA. The RNA molecules that contain this material can be separated from the rest of the polysomal RNA by differential phenol extraction with neutral and alkaline Tris buffers. Synthetic poly(A) exhibits the same behavior as the rapidly-labeled polysomal RNA with respect to Millipore binding and phenol fractionation. The characteristics of the rapidly-labeled polysomal RNA component permit its isolation free of ribosomal RNA.

Adenine Nucleotides↗
PubMed1971

Attachment of ribosomes to membranes during polysome formation in mouse sarcoma 180 cells.

Addition of nutrients to starved mouse S-180 cells leads to rapid conversion of ribosomal monomers to polysomes. During this process, a portion of the ribosomes originally found in the 17,000 g (10 min centrifugation) supernatant of cell lysates becomes firmly attached to structures sedimenting at 500 g (5 min centrifugation). Electron microscopy of sections of the intact cells showed the change from randomly distributed ribosomal particles to clusters. Association with membranes also became evident. The material sedimenting at 500 g comprised nuclei enclosed in an extensive endoplasmic reticulum (ER) network. This fraction prepared from recovering cells showed numerous ribosome clusters associated with the ER network. The appearance of many of these clusters indicated that the ribosomal particles were not directly bound to the membranes. RNase treatment released about 40% of the attached ribosomes as monomers, and ethylenediaminetetraacetic acid released 60% as subunits. It is suggested that during polysome formation a portion of the ribosomes becomes attached to the membranes through the intermediary of messenger RNA.

Animals↗