CONSERVED ALTERNATIVE SPLICING PATTERNS AND SPLICING SIGNALS IN THE DROSOPHILA SODIUM-CHANNEL GENE PARA

We cloned genomic DNA corresponding to the Drosophila virilis homologu e of para, a gene encoding a sodium channel alpha-subunit, and obtaine d many partial cDNA clones from embryos and adults. Para protein has b een well conserved, and the optional elements at six different sites o f alternative splicing in D. melanogaster are present in D. virilis, i n addition to one new optional exon. Among 31 different splice-types o bserved in D. virilis, the stage-specific pattern of alternative splic ing seen in D. melanogaster is also conserved. Comparison of genomic D NA sequence revealed three aspects that vary between alternatively and constitutively used exon sequences. Sixteen short blocks (10-75 bp), the only recognizably conserved intron sequence, were disproportionate ly associated with alternatively used splice sites. Silent site substi tutions were found much less frequently in alternative than constituti ve exon elements, and the degree of match to the Drosophila splice sit e consensus tended to be lower at less frequently selected alternative splice junctions. This study shows that the developmentally regulated variability of para products is highly conserved and therefore likely to be of functional significance and suggests that a variety of diffe rent sequence-dependent mechanisms may regulate this pattern of altern ative splicing.