Proteolytic activation of both components of the cation stress-responsive Slt pathway in Aspergillus nidulans.
Tolerance of Aspergillus nidulans to alkalinity and elevated cation concentrations requires both SltA and SltB. Transcription factor SltA and the putative pseudokinase/protease signaling protein SltB comprise a regulatory pathway specific to filamentous fungi. In vivo, SltB is proteolytically cleaved into its two principal domains. Mutational analysis defines a chymotrypsin-like serine protease domain that mediates SltB autoproteolysis and proteolytic cleavage of SltA. The pseudokinase domain might modulate the protease activity of SltB. Three forms of the SltA transcription factor coexist in cells: a full-length, 78-kDa version and a processed, 32-kDa form, which is found in phosphorylated and unphosphorylated states. The SltA32kDa version mediates transcriptional regulation of sltB and, putatively, genes required for tolerance to cation stress and alkalinity. The full-length form, SltA78kDa, apparently has no transcriptional function. In the absence of SltB, only the primary product of SltA is detectable, and its level equals that of SltA78kDa. Mutations in sltB selected as suppressors of null vps alleles and resulting in cation/alkalinity sensitivity either reduced or eliminated SltA proteolysis. There is no evidence for cation or alkalinity regulation of SltB cleavage, but activation of sltB expression requires SltA. This work identifies the molecular mechanisms governing the Slt pathway.
Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas, CSIC, 28040 Madrid, Spain.
Laura
L
Mellado
Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas, CSIC, 28040 Madrid, Spain Section of Microbiology, Imperial College London, London SW7 2AZ, United Kingdom.
Herbert N
HN
Arst
Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas, CSIC, 28040 Madrid, Spain eespeso@cib.csic.es.
Eduardo A
EA
Espeso
D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000201:enzymology / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D005658:Fungi / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D000072417:Protein Domains; D059748:Proteolysis; D055049:Salt Tolerance / Q000502:physiology*; D057057:Serine Proteases / Q000378:metabolism*; D015398:Signal Transduction; D013312:Stress, Physiological / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism*
C530975:CrzA protein, Aspergillus fumigatus; D005656:Fungal Proteins; C092394:PacC protein, Aspergillus; D014157:Transcription Factors; D057057:Serine Proteases