Figure 2.

Effect of U1 RNA elongation on RNA export. (A) A ³²P-labeled mixture of U1 RNA derivatives, containing 50 nt (+50 nt), 100 nt (+100 nt), 200 nt (+200 nt), or 300 nt (+300 nt) sequence from DHFR mRNA, was microinjected into Xenopus oocyte nuclei together with DHFR mRNA, U1 ΔSm, U5 ΔSm, and U6 Δss RNAs. All the RNAs except U6 were m7G-capped. The effects of PHAX and BSA–NES proteins were examined as in Figure 1B. (B) Quantitation of RNA export from three independent experiments as in A. Averages and standard deviations with BSA–NES (gray bars) or BSA-mut (black bars), or without proteins (buffer; white bars) are shown. (C) The same as in B except that PHAX WT (gray bars) or PHAX ΔNES (black bars) proteins were used. (D–F) The same as in A–C except that β-globin mRNA sequences were inserted instead of DHFR sequences. (G) The same as B and E except that ftz mRNA were used as the insert. Only quantitation is shown. (H) Effect of an mRNA competitor on RNA export. The same RNA mixture as in G was microinjected either with 0.5 pmole of unlabeled uncapped DHFR mRNA (DHFR comp., 500 times excess over labeled RNAs) or without it (buffer).