During the late phase of subgroup C
adenovirus infection, export of cellular
mRNA from the nucleus to the cytoplasm is inhibited. In one approach to investigate the mechanism whereby viral late mRNAs are selected for export, we have examined the metabolism of small cellular
RNA species transcribed by all three
RNA polymerases during the late phase of Ad5
infection. No changes in the quantities of [3H]
uridine-labeled
5S rRNA or tRNAs entering the cytoplasm were observed in infected cells. Adenovirus type 5
infection reduced the nuclear and cytoplasmic populations of the newly synthesized,
snRNP-associated snRNAs U1, U2, U4, U5, and U6. Transcription of a representative
snRNA,
U1 RNA, was not inhibited, indicating that the post-transcriptional metabolism of snRNAs was perturbed during the late phase of
infection. The increased cytoplasmic concentration of newly synthesized
U1 RNA in Ad5- compared to mock-infected cells, and the greater reduction of the
snRNP-associated compared to the total
U1 RNA population, indicated that
snRNP assembly in the cytoplasm was impaired. As
adenovirus infection does not perturb export from the nucleus of small cellular mRNAs transcribed by
RNA polymerases II and III, viral
mRNA must be distinguished for selective export at a nuclear step upstream of translocation to the cytoplasm via nuclear pore complexes.