DISTRIBUTION OF CYTOPLASMIC POLY(A+)RNA SEQUENCES IN FREE MESSENGER-RIBONUCLEOPROTEIN AND POLYSOMES OF MOUSE ASCITES-CELLS

The cytoplasmic non-polysomal poly(A+)mRNA found in the free messenger ribonucleoprotein of mouse Taper ascites cells was demonstrated by nucleic acid hybridization to contain only about 400 different mRNA sequences, in contrast to the greater than the 8000 sequences of the total cytoplasm. Approximately 50% by mass of the free RNP‡ ‡ Abrreviation used: RNP, ribonucleoprotein; cDNA. complementary DNA.-mRNA was shown to consist of only 15 different mRNA sequences and the other 50% to represent 400 different mRNA sequences. The abundant free mRNP sequences were also present in the polysomes at one-tenth of their concentration in the free mRNP. The 400 less abundant free RNP-mRNAs were found to be in the middle abundant class of total cytoplasmic sequences. The 400 less abundant free RNP-mRNA sequences were also found on the polysomes: 50% of these sequences were at similar concentrations in the polysomes as in the free mRNP, while 50% were found in the polysomes at reduced concentrations. Thus it is concluded that these mouse tumor cells maintain a highly polarized distribution of certain subsets of mRNA species between the functioning (polysomes) and non-functioning (free mRNP) compartments of the cytoplasm. © 1979.