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Circular extrachromosomal DNA codes for a surface protein in the (+) mating type of the zygomycete Absidia glauca
1Institut für Genbiologische Forschung, Berlin, Federal Republic of Germany.
Abstract:
A small protein with a molecular mass of 15 kDa, which is specifically found on the hyphal surface of a (+) mating-type strain of the model zygomycete Absidia glauca, was purified to electrophoretic homogeneity and partially sequenced. The corresponding gene was cloned by means of an oligonucleotide probe deduced from the protein sequence. It could be localized on an extrachromosomal circular DNA element with a total length of 1250 bp. Electron microscopic analysis of A. glauca DNA showed that small extrachromosomal DNAs with varying length are a common feature of this zygomycete. There are no indications of additional chromosomal copies of the gene for this surface protein, and the plasmid is absent from DNA preparations of the (-) mating type. The copy number ranges around three per haploid genome, and a single transcript with a length of 400 bp, coding for the surface protein, could be found by employing a hybridization probe which spans the complete fungal plasmid. This is the first report of naturally occurring extrachromosomal DNA in a Mucor-like fungus, and the only example where an integral protein of the cell wall is encoded by a plasmid.
Insights
Researchers discovered a novel surface protein in the fungus Absidia glauca, encoded by a unique plasmid. This extrachromosomal DNA is specific to the (+) mating type, marking a significant finding in fungal genetics.
Area of Science:
- * Mycology
- * Molecular Biology
- * Fungal Genetics
Background:
- * The model zygomycete Absidia glauca is studied for its unique biological characteristics.
- * Cell surface proteins play crucial roles in fungal interactions and development.
- * Extrachromosomal DNA elements are not commonly reported in Mucor-like fungi.
Purpose of the Study:
- * To identify and characterize a specific hyphal surface protein from Absidia glauca.
- * To determine the genetic basis and location of the gene encoding this surface protein.
- * To investigate the presence and nature of extrachromosomal DNA in Absidia glauca.
Main Methods:
- * Protein purification via electrophoresis.
- * Partial protein sequencing.
- * Gene cloning using oligonucleotide probes.
- * DNA isolation and electron microscopy.
- * Southern blot hybridization for gene localization and copy number determination.
Main Results:
- * A 15 kDa surface protein was purified from the (+) mating type strain of Absidia glauca.
- * The gene for this protein resides on a 1250 bp extrachromosomal circular DNA element (plasmid).
- * This plasmid is absent in the (-) mating type strain and present at approximately three copies per haploid genome.
- * A single 400 bp transcript for the surface protein was detected.
- * Small extrachromosomal DNAs are common in Absidia glauca.
Conclusions:
- * This study reports the first instance of naturally occurring extrachromosomal DNA in a Mucor-like fungus.
- * It provides the sole known example of an integral cell wall protein being encoded by a plasmid.
- * The findings highlight the role of plasmids in encoding cell surface components in specific fungal mating types.