Fil1, a G-protein alpha-subunit that acts upstream of cAMP and is essential for dimorphic switching in haploid cells of Ustilago hordei.
A constitutive mutation, fil1, that causes filamentous growth in the haplophase of the dimorphic smut fungus Ustilago hordei, was previously shown to be genetically associated with a 50-kb deletion within a 940-kb chromosome. Physiological studies suggested that a gene that functions upstream of adenylyl cyclase was deleted in the mutant. Representational difference analysis of isolated chromosomes was used to obtain deletion-specific DNA probes and corresponding genomic cosmid clones. Complementation analysis identified a cosmid clone and subsequently a 2.1-kb insert that converted transformants of the mutant strain 10.1a(fil1) from the filamentous to the sporidial cell type. A single open reading frame of 354 codons that encodes a putative alpha-subunit of the heterotrimeric G-proteins was identified. Fil1 displayed a high degree of sequence identity to Gpa1 from the basidiomycete Cryptococcus neoformans and CPG-2 from the ascomycete Cryphonectria parasitica. FIL1, when introduced on a self-replicating vector, was found to suppress filamentous growth of starved haploid wild-type strains and restore normal mating response to the fil1 mutant, but did not suppress sexual dimorphism of either strain. Fil1 appears to function analogously to mammalian G alpha proteins, which are coupled to cAMP production via adenylyl cyclase, to regulate dimorphic switching in U. hordei.
Lichter
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Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902, USA.
Mills
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D000595:Amino Acid Sequence; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism*; D004271:DNA, Fungal; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006238:Haploidy; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014588:Ustilago / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D004271:DNA, Fungal; D005656:Fungal Proteins; D000242:Cyclic AMP; D019204:GTP-Binding Proteins