Abstract
Lysates of rabbit reticulocytes and other mammalian cells are known to contain an activity which binds with high specificity ppp(A2′p) 3A,3′-[ 32P]pCp. The binding activity shows a marked dependence on preincubation of lysates at different termperatures (4°C – 45°C). For example, binding was increased 50% by preincubation of rabbit reticulocyte lysates at 37°C for 60 minutes. An identical preincubation of mouse brain extracts results in a greater than 90% loss of binding activity. Fractionation of rabbit reticulocyte lysates into the postribosomal supernatant (PRS) and the ribosomal salt wash (RSW), followed by heparin-agarose column chromatoraphy, showed that with the PRS fraction, most of the binding activity is eluted with 600 mM KCl. With the RSW fraction, more than 50% of the binding activity is eluted with 250 mM KCl. These data suggest that multiple ppp(A2′p) nA binding protein activities exist in mammalian cells.
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