Two distinct pathways for intronless mRNA expression: one related, the other unrelated to human immunodeficiency virus Rev and human T cell leukemia virus type I Rex functions.

Intronless mRNAs were classified into two classes based on the sensitivities of their expression to the inhibitory effect of TAgRex, a dominant-negative mutant of the Rex protein of human T cell leukemia virus type I, and their abilities to express the genes encoded in the intron of the human immunodeficiency virus (HIV) genome. Interferon-alpha mRNA could not induce the expression of the env gene of HIV, and its expression was resistant to TAgRex. In contrast, the posttranscriptional regulatory element (PRE), necessary for the nucleo-cytoplasmic export of mRNAs of hepatitis B virus, induced expression of the chloramphenicol acetyl transferase gene located within the intron of the HIV genome. PRE-mediated expression was inhibited by TAgRex. Thus, these results suggest that there are at least two distinct pathways for intronless mRNA expression, one related to and the other unrelated to Rev and Rex functions.