At elevated temperatures, the Neurospora crassa mutant colonial, temperature-sensitive 3 (cot-3) forms compact, highly branched colonies. Growth of the cot-3 strain under these conditions also results in the loss of the lower molecular weight (LMW) isoform of the Ser/Thr protein kinase encoded by the unlinked cot-1 gene, whose function is also involved in hyphal elongation. The unique cot-3 gent has been cloned by complementation and shown to encode translation elongation factor 2 (EF-2). As expected for a gene with a general role in protein synthesis, cot-3 mRNA is abundantly expressed throughout all asexual phases of the N. crassa life cycle. The molecular basis of the cot-3 mutation was determined to be an ATT to AAT transversion, which causes an Ile to Asn substitution at residue 278. Treatment with fusidic acid (a specific inhibitor of EF-2) inhibits hyphal elongation and induces hyper-branching in a manner which mimics the cot-3 phenotype, and also leads to a decrease in the abundance of the LMW isoform of COT1. This supports our conclusion that the mutation in cot-3 which results in abnormal hyphal elongation/branching impairs EF-2 function and confirms that the abundance of a LMW isoform of COT1 kinase is dependent on the function of this general translation factor.

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Keywords Cot-3, Elongation factor 2, Fusidic acid, Hyphal branching, Neurospora crassa
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Journal MGG Molecular & General Genetics
Propheta, O., Vierula, J., Toporowski, P., Gorovits, R., & Yarden, O. (2001). The Neurospora crassa colonial temperature-sensitive 3 (cot-3) gene encodes protein elongation factor 2. MGG Molecular & General Genetics, 264(6), 894–901. doi:10.1007/s004380000379