FIG. 6.

One nucleotide in the 5′ UTR of α-tubulin is critical for splicing. The upper sequence shows the endogenous α-tubulin 5′ UTR. Sequences are shown from the −4 position relative to the 3′SS, and all constructs contain the α-tubulin UR. Only the 5′ UTR sequences differ. pNS10/56 contains the procyclin 5′ UTR lacking cryptic AG sites. In pNS10/72, 8 nt downstream of the 3′SS have been changed to match the sequence found in the endogenous α-tubulin 5′ UTR. pNS10/73 contains a 5′ UTR sequence identical to the α-tubulin 5′ UTR for 20 nt downstream of the 3′SS, except for the omission of nucleotides at positions +1 and +2. pNS10/74 is identical to pNS10/73 but with the +1 and +2 nucleotides intact. In pNS10/75, the AG within the 5′ UTR of pNS10/74 was changed to AA.