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A purification procedure is described for the initiation factors of protein synthesis from rabbit reticulocytes: (a) from the ribosomal wash and (b) from the postribosomal supernantant. A comparison is made between these preparations with respect to yield and specific activity. eIF-4A and eIF-4D occur mainly in the postribosomal supernatant; eIF-2, eIF-4C and eIF-5 are more evenly divided over both fractions, whereas eIF-1, eIF-3 and eIF-4B are found almost exclusively in the ribosomal wash. No significant difference in specific activity could be detected when factors from both sources were compared, with a possible exception of eIF-4A and eIF-4D.
Thomas et al. (1979) studied this question.