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Extreme nuclear disproportion and constancy of enzyme activity in a heterokaryon of Neurospora crassa

Pitchaimani, Kandasamy and Maheshwari, Ramesh (2003) Extreme nuclear disproportion and constancy of enzyme activity in a heterokaryon of Neurospora crassa. In: Journal of Genetics, 82 (1 & 2). pp. 1-6.

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Abstract

Heterokaryons of Neurospora crassa were generated by transformation of multinucleate conidia of a histidine-3 auxotroph with $his-3^+$ plasmid. In one of the transformants, propagated on a medium with histidine supplementation, a gradual but drastic reduction occurred in the proportion of prototrophic nuclei that contained an ectopically integrated $his-3^+$ allele. This response was specific to histidine. The reduction in prototrophic nuclei was confirmed by several criteria: inoculum size test, hyphal tip analysis, genomic Southern analysis, and by visual change in colour of the transformant incorporating genetic colour markers. Construction and analyses of three-component heterokaryons revealed that the change in nuclear ratio resulted from interaction of auxotrophic nucleus with prototrophic nucleus that contained an ectopically integrated $his-3^+$ gene, but not with prototrophic nucleus that contained $his-3^+$ gene at the normal chromosomal location. The growth rate of heterokaryons and the activity of histidinol dehydrogenase—the protein encoded by the $his-3^+$ gene—remained unchanged despite prototrophic nuclei becoming very scarce. The results suggest that not all nuclei in the coenocytic fungal mycelium may be active simultaneously, the rare active nuclei being sufficient to confer the wild-type phenotype.

Item Type: Journal Article
Additional Information: The Copyright belongs to Indian Academy of Sciences.
Keywords: Neurospora crassa;Heterokaryon;Nuclear ratio;Histidinol dehydrogenase;Transformation
Department/Centre: Division of Biological Sciences > Biochemistry
Date Deposited: 13 Apr 2006
Last Modified: 19 Sep 2010 04:25
URI: http://eprints.iisc.ernet.in/id/eprint/6264

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