Micro-processing events in mRNAs identi®ed by DHPLC analysis

Post-transcriptional processes such as alternative splicing and RNA editing have a huge impact on the diversity of the proteome. Detecting alternatively spliced transcripts is dif®cult when they are rare. In addition, edited transcripts often differ from the genomic sequence by only a few nucleotides. Denaturing high performance liquid chromatography (DHPLC) is routinely used for single nucleotide polymorphism detection and we used this method to detect alternatively spliced or edited transcripts. As the sites of RNA editing appear to be conserved within gene families, we investigated whether editing sites are conserved in the murine homologue of the Drosophila cacophony transcript encoding the a1 subunit of a voltage-gated calcium channel that is edited at 10 independent positions. Although DHPLC analysis detects RNA editing at as low as 3% in control transcripts, no evidence of RNA editing was found in the analysed murine transcript. However an alternative exon was identi®ed at the 3¢ end of the mouse Cacna1a transcript and an alternative micro-exon encoding only two amino acids (NP) was found in the extracellular loop before the IVS4 helix in the same transcript. In the homologous Drosophila transcript a micro-exon also encoding two amino acids was found at the same position before the IVS4 helix.