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Isolation and characterization of a calmodulin-encoding cDNA from the pathogenic fungus Histoplasma capsulatum
1University of Southern Mississippi, Department of Biological Sciences, Hattiesburg 39406-5018, USA.
Abstract:
We describe in this paper the isolation and complete sequence of a calmodulin (CaM) encoding cDNA from the dimorphic pathogenic fungus Histoplasma capsulatum (GenBank accession U12505). The deduced amino acid sequence was identical to the CaM of Aspergillus nidulans and had only one amino acid difference from the CaM of Neurospora crassa. Saccharomyces cerevisiae CaM, however, has only about 60% amino acid identity compared with H. capsulatum. These data further support the close relationship of Histoplasma to the filamentous ascomycetes. Histoplasma CaM was expressed as a single major transcript of approximately 1200 nt. in both the yeast and mould growth forms. CaM mRNA levels were approximately two-fold greater in the yeast than in the mould form of the organism. Southern blot analysis indicated that the H. capsulatum CaM gene is present in a single copy.
Insights
Researchers isolated and sequenced calmodulin (CaM) from Histoplasma capsulatum, revealing its close relationship to filamentous fungi. CaM mRNA levels were higher in the yeast form, suggesting differential gene expression.
Area of Science:
- Mycology
- Molecular Biology
- Biochemistry
Background:
- Calmodulin (CaM) is a crucial calcium-binding protein involved in regulating various cellular processes.
- Understanding CaM in pathogenic fungi like Histoplasma capsulatum is vital for comprehending fungal biology and pathogenesis.
Purpose of the Study:
- To isolate and determine the complete nucleotide sequence of the calmodulin-encoding cDNA from Histoplasma capsulatum.
- To analyze the deduced amino acid sequence and compare it with CaM from other fungal species.
- To investigate the expression patterns and gene copy number of calmodulin in Histoplasma capsulatum.
Main Methods:
- Isolation and sequencing of calmodulin cDNA from Histoplasma capsulatum.
- Deduced amino acid sequence analysis and comparison with homologous proteins.
- Northern blot analysis to study transcript levels in different growth forms.
- Southern blot analysis to determine gene copy number.
Main Results:
- The complete sequence of Histoplasma capsulatum calmodulin (CaM) cDNA was obtained.
- The deduced amino acid sequence showed high identity to Aspergillus nidulans CaM and close similarity to Neurospora crassa CaM, supporting a relationship with filamentous ascomycetes.
- Histoplasma CaM is expressed as a single transcript of approximately 1200 nt in both yeast and mould forms.
- CaM mRNA levels were approximately two-fold higher in the yeast form compared to the mould form.
- Southern blot analysis confirmed the calmodulin gene is present as a single copy in the Histoplasma capsulatum genome.
Conclusions:
- The findings confirm the close evolutionary relationship between Histoplasma and filamentous ascomycetes based on calmodulin sequence homology.
- Differential expression of calmodulin mRNA between yeast and mould forms suggests a role in regulating dimorphism in Histoplasma capsulatum.