Abstract
The model filamentous fungus Neurospora crassa has been studied for over fifty years and many temperature-sensitive mutants have been generated. While most of these have been mapped genetically, many remain anonymous. The mutation in the N. crassa temperature-sensitive lethal mutant un-7 was identified by a complementation based approach as being in the open reading frame designated NCU00651 on linkage group I. Other mutations in this gene have been identified that lead to a temperature-sensitive morphological phenotype called png-1. The mutations underlying un-7 result in a serine to phenylalanine change at position 273 and an isoleucine to valine change at position 390, while the mutation in png-1 was found to result in a serine to leucine change at position 279 although there were other conservative changes in this allele. The overall morphology of the strain carrying the un-7 mutation is compared to strains carrying the png-1 mutation and these mutations are evaluated in the context of other temperature-sensitive mutants in Neurospora.
Highlights
While the genetic map of the filamentous fungus N. crassa contains over 1,200 markers [1], the genome sequence predicts closer to 10,000 genes for this organism [2]
We have demonstrated that the open reading frame (ORF) mutated in un-7 is related to a yeast gene whose product is implicated in the targeting of misfolded proteins for degradation by the proteosome, recent studies have challenged this role in Neurospora [7,8]
A relatively random selection of TS lethal mutants has led to a group of mutants that impact various steps of the protein synthesis, trafficking, and quality control suggesting that this might be a common characteristic of the TS mutants in Neurospora generated by Inoue and colleagues [4]
Summary
While the genetic map of the filamentous fungus N. crassa contains over 1,200 markers [1], the genome sequence predicts closer to 10,000 genes for this organism [2]. A relatively random selection of TS lethal mutants has led to a group of mutants that impact various steps of the protein synthesis, trafficking, and quality control suggesting that this might be a common characteristic of the TS mutants in Neurospora generated by Inoue and colleagues [4]. This is in stark contrast to the distribution of other TS mutations in Neurospora which affect a variety of biological functions, including TS auxotrophs and TS morphological mutants. The characterization of both TS lethal and TS morphological mutations in the same gene in Neurospora emphasizes the value of traditional mutant hunts
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