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 columns^1–3. 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 reticulocytes^5,6, 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.