Messenger RNA for globin in the postribosomal supernatant of rabbit reticulocytes

10S RNA has been isolated from the postribosomal supernatant of rabbit reticulocyte lysate. This RNA is associated with protein in a ribonucleoprotein particle that sediments at approximately 20S. The 10S RNA extracted from this particle codes predominantly for alpha globin chains when it is translated by a mouse ascites cell-free extract. The product of the cell-free synthesis has been characterized by column chromatography and electrophoresis of the tryptic peptides. About 20% of the total alpha chain mRNA is present in the postribosomal supernatant, whereas beta chain mRNA is almost exclusively associated with polyribosomes.