Alternative splicing of fructose 1,6-bisphosphate aldolase transcripts in Drosophila melanogaster predicts three isozymes.

The genes that encode fructose 1,6-bisphosphate aldolase of Drosophila melanogaster have been isolated and characterized. These genes exist in a single copy 8-kilobase pair locus in the Drosophila genome which is located at cytogenetic position 97A-B. The nucleotide sequence and transcript mapping suggest that three overlapping protein isozyme genes may be encoded at this locus. These isozyme genes all share a single promoter, a 5'-untranslated first exon, and two other protein coding exons. The isozyme-specific carboxyl-terminal amino acids are encoded by one of three alternatively utilized fourth exons: 4A, 4B, or 4C by alternative splicing. The transcript containing exon 4C, whose sequence has been reported previously, is abundant throughout development and has a developmental profile similar to other glycolytic gene transcripts; however, it shows developmental specificity in the alternative use of two polyadenylation signals which result in a 2.4-kilobase and a 1.9-kilobase transcript. The transcript containing exon 4B is 1.6 kilobases in size and is most abundant during the larval stages and during the time of eclosion. The transcript containing exon 4A is in low abundance and found only during the adult stage. Sequence comparisons of the alternative fourth exons indicate that the duplication leading to the multiple exons is quite old and preceded the origin of the genus Drosophila.

Structure and expression of the triose phosphate isomerase (Tpi) gene of Drosophila melanogaster.

We report the isolation of the genomic sequence that encodes the enzyme triose phosphate isomerase of Drosophila melanogaster. There is a single copy of the Tpi sequence in the genome of Drosophila, as judged by Southern blots and in situ hybridization to salivary gland chromosomes. The sequence of 3414 nucleotides from the Tpi region was determined. The gene has an intron in the 5' untranslated region of the transcript and a second intron in the coding region at an evolutionarily conserved position. Transcripts initiate at a single site which does not have a TATA box in the usual position. Northern blot analysis of RNA prepared from different developmental stages revealed that Tpi mRNA is present in substantial amounts in oocytes, declines in abundance in early embryos, and begins to increase during mid-embryogenesis. Transcript abundance follows a pattern typical of enzymes involved in intermediate metabolism. A peak is found during third instar followed by a decline during pupal stages and then a second rise near the time of eclosion.