A major species of mammalian messenger RNA lacking a polyadenylate segment.

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Abstract
Translation of total polysomal RNA from sarcoma 180 ascites cells in a wheat germ cell-free system produces 2 major polypeptides, A and B, with MW of 50,000 and 45,000, respectively. Fractionation on Millipore filters or on oligo(dT)-cellulose leads to retention of the mRNA specific for protein A in the poly(A)-containing fraction and to accumulation of the B mRNA in the unadsorbed poly(A)-deficient fraction. The mRNA for B sediments at approximately 18 S; it is released as a 50 S ribonucleoprotein on EDTA treatment of polysomes. Its translation is particularly sensitive to an inhibitor present in the polysomal RNA. The poly(A)-deficient mRNA for the 45,000 dalton polypeptide is also present in mouse myeloma MPC-11 cells, where it seems to be localized in membrane-bound polysomes.