FIG. 2.

Deletions within the μs poly(A) signal reduce but do not eliminate its use. (A) Sequence of the μs poly(A) signal (Cμ) and the 11-nt deletion (pA11) and 21-nt deletion (pA21) encompassing the AAUAAA core upstream element; the sequences deleted from pA11 and pA21 are bracketed below the Cμ sequence. The cleavage sites for Cμ, pA11, and pA21 were identified using construct-specific S1 nuclease probes and are shown by the arrowheads above each sequence. The core upstream elements or sequences that may fulfill the role of this element in each construct are underlined; the downstream GU-rich sequences are shown in uppercase letters. (B) S1 nuclease analysis of RNA from M12 B cells (B) and S194 plasmacytoma cells (PC) transiently transfected with the constructs shown above each lane. The probe used was from the wild-type sequence, and the bands protected by the pA11 and pA21 RNA are smaller because the sequence of the RNA diverges from the probe at the site of the deletion. (C) Summary of the μs mRNA-to-μm mRNA expression ratios (pA/splice) for these constructs, compiled from at least two S1 nuclease analyses of two independent transfections.