An unstable mutant gene of the am locus of Neurospora results from a small duplication.
We have cloned the unstable am mutant gene, am126, as well as the am gene from an am126 revertant. The mutation is a result of a 33-bp duplication that repeats a sequence starting 13 bp upstream of the 3' splice junction between intron 1 and exon 2 and extends 20 bp into exon 2. In addition, there is a G----A transition 2 bp upstream of the first copy of the duplicated sequence. In the revertant gene the wild-type sequence is precisely recovered, involving both the loss of the duplication and a reversion (A----G) of the associated transition. Our data suggest that only the more 5' of the two 3' splice junctions present in the duplicated version of the gene is used. This favors a 5'----3' scanning mechanism for exon splicing.
D001483:Base Sequence; D004271:DNA, Fungal / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics*; D005800:Genes, Fungal; D005969:Glutamate Dehydrogenase / Q000235:genetics*; D018086:Glutamate Dehydrogenase (NADP+); D009154:Mutation; D009491:Neurospora / Q000235:genetics*; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics*
D004271:DNA, Fungal; D005656:Fungal Proteins; D005969:Glutamate Dehydrogenase; D018086:Glutamate Dehydrogenase (NADP+)