Adenine-rich polymer associated with rabbit reticulocyte messenger RNA.

Abstract

POLYPURINES have been isolated from subcellular fractions of mouse liver by a method which involves a limited nuclease digestion of the RNA, followed by chromatography of the digestion products on polystyrene columns1–3. These polypurines consist of clusters of adenylic acid and guanylic acid in which the A/G ratio is 2–10; the materials isolated from the rough endoplasmic reticulum have sedimentation coefficients of 3–5S, but a molecule containing twenty nucleotides can be obtained from the free polysomes4. The latter polymer is part of a rapidly labelled RNA species that sediments between the 32S subunit and 5S RNA when EDTA-treated polysomes are centrifuged on a sucrose density gradient. With longer times of labelling with 32P the polymer is also found in association with the 32S subunit. It seems likely that the adenine-rich polymer is found in close association with messenger-like RNA. These obssrvations prompted us to investigate the polypurine content of a better characterized mammalian messenger RNA. Such an RNA is the haemoglobin messenger RNA which has been isolated from rabbit reticulocytes5,6, and purified by polyacrylamide gel electrophoresis7. This species of RNA8 and a similar RNA from mouse reticulocytes9 have been demonstrated to initiate specific globin synthesis in vitro. We now describe the isolation of an adenine-rich polymer from purified messenger RNA obtained from rabbit reticulocyte polysomes and its relationship to the size of the ribosomes from which the messenger RNA is derived.