Antibodies to Nup153 have a long-lasting and specific inhibitory effect on mRNA export but fail to block tRNA export. (A) An injection experiment was performed as described in Figure 1, except that, in some cases, a recombinant fragment of Nup153 was coinjected with the first injection of buffer or antibodies (lanes 5–8). The mix of RNAs in this experiment included tRNA in addition to pre-mRNA and U1 snRNA. Antibodies to Nup153 did not prevent tRNA export (compare lanes 2 and 4), whereas, as before, export of mRNA and U1 snRNA was blocked by these antibodies. When the Nup153 fragment was coinjected with anti-Nup153 antibodies (lanes 7 and 8), the effect of the antibody was neutralized (lane 8). (B) After injection of either buffer or antibodies, oocytes were injected with a mixture of pre-mRNA, U1 snRNA, 5S RNA, and U6 snRNA and then harvested after either 2 h (lanes 1–4) or 16 h (lanes 5–8) of incubation at 18°C. U6 snRNA is relatively less stable and is no longer detected at the later time point. Export of mRNA, U1 snRNA, and 5S RNA was inhibited at both early and late time points in oocytes preinjected with antibodies to Nup153.