Fig. 2. RT-PCR analysis of syntaxin isoform expression in RPE-J cells. mRNA of syntaxin 3 and of different alternatively spliced isoforms of syntaxin 2 were amplified by RT-PCR. For syntaxin 2 isoform determination, two primer pairs were used that had been previously shown to distinguish between isoforms 2A, 2B, 2C and 2D (Quinones et al., 1999). Primer combination 2₁ generates the following PCR products: syntaxin 2A (200 bp), 2D (228 bp), no products for syntaxin 2B and 2C. Primer combination 2₂ generates the following PCR products: syntaxin 2A (700 bp), 2B (600 bp), 2C (170 bp), 2C 170 bp), 2D (728 bp). The respective positions of the different products are indicated by arrows. A shows that transcripts for syntaxin 2A, B and C can be detected in rat kidney. Rat brain expresses all four syntaxin 2 isoforms as previously reported. As shown in B, reaction products for syntaxins 2A and 2B were detected from RPE-J cells but not 2C, 2D. For the detection of syntaxin 3A transcripts, a single primer pair was used. B shows that syntaxin-3A-specific reaction product was detected in the positive control (lane `syn3', rat syntaxin 3A cDNA as template), whereas no syntaxin 3A product could be detected from RPE-J cells. As a negative control, no products were detected in samples that were not reverse transcribed (-RT).