Alterations in the size of the poly(a) segment in newly-synthesized messenger RNA of mouse sarcoma 180 ascites cells.

The size of the poly(A) segment present at the 3'-end of mRNA molecules decreases gradually after entry of the mRNA into the cytoplasm. The size reduction seems to occur equally in free and polysome-bound mRNA. It is not affected by conditions that inhibit protein synthesis, such as treatment with cycloheximide and amino acid deprivation. The latter condition leads to a substantial increase in the size of nuclear poly(A). The rate of poly(A) cleavage could determine the length of time a mRNA molecule remains functional in the cytoplasm.