Adenovirus type 2 fiber mRNA synthesis: no evidence for a cytoplasmic processing pathway.

Adenovirus type 2 fiber mRNA exists in several forms in the cytoplasm which differ in the presence or absence of extra 5'-leader segments (L. T. Chow and T. R. Broker, Cell 15:497-510, 1978). We have investigated the possibility that forms possessing extra leader segments serve as precursors to the mature form in the cytoplasm. Pulse-labeled fiber mRNA became considerably shorter (150 to 250 bases) during a chase; however, most of the pulse-labeled species failed to hybridize to DNA fragments known to encode extra leader segments. Moreover, the entire decrease in size appeared to be due to extensive shortening of the polyadenylic acid tail. Mature-sized fiber mRNA was synthesized normally in cells infected with the nondefective adenovirus type 2-simian virus 40 hybrid virus Ad2+ND5, in which the region encoding the extra leader segments is deleted. These results indicate that the additional 5'-leader segments present in wild-type adenovirus type 2 fiber mRNA are not required for the production of mature fiber mRNA and that species that possess them are not cytoplasmic precursors to the mature form.