Newly formed mRNA lacking polyadenylic acid enters the cytoplasm and the polyribosomes but has a shorter half-life in the absence of polyadenylic acid.

Labeled adenovirus type 2 nuclear RNA molecules from cells treated with 3'-deoxyadenosine (3'dA) were earlier reported to lack polyadenylic acid [poly(A)], but to be correctly spliced in the nucleus (M. Zeevi et al., Cell 26:39-46, 1981). We have now found that the shortened mRNA molecules, lacking poly(A), can also be found in the cytoplasm of 3'dA-treated cells in association with the polyribosomes. In addition, the accumulation of labeled, nuclear adenovirus-specific RNA complementary to early regions 1a, 1b, and 2 of the adenovirus genome was approximately equal in 3'dA-treated and control cells. At the initial appearance of newly labeled adenovirus type 2 RNA (10 min) in the cytoplasm, there was one-half as much labeled RNA in 3'dA-treated cells as in the control. However, control cells accumulated additional mRNA in the cytoplasm very rapidly in the first 40 min of labeling, whereas the 3'dA-treated cells did not. Therefore, it appears that the correctly spliced, poly(A)- mRNA molecules that are labeled in the presence of 3'dA can be transported from the nucleus with nearly the same frequency and the same exit time as in control cells and can be translated in the cytoplasm but have a much shorter half-life than the poly(A)+ mRNA molecules from control infected cells. From these results it is suggested that the role of poly(A) may be entirely to increase the longevity of cytoplasmic mRNA.