Figure 4.

(A) Polyadenylation sites within or near SIRE. Arrows point out poly(A) addition sites as they were identified in cDNAs containing SIRE. The black box within SIRE represents region II; in region III, py-AG indicates the position of SIRE's trans-splicing signal (9). (B) Schematic representation of five different situations where transcribed SIRE sequences are found: lanes 1, in the 3′ UTR, SIRE provides the poly(A) addition site; 2, in the 3′ UTR, poly(A) addition immediately after SIRE; 3, in the 5′ UTR when SIRE acts as a trans-splicing signal donor (9); 4 and 5, SIRE provides the codons that encode the C-terminal end of ORFs (hatched boxes). The ORFs N4 and RH are not depicted in scale. SL boxes represent SL sequences.