PolyT Variation Within Mitochondrial ProteinCod

Authors: Angelique H Riepsamen Vivian C Blok Mark Phillips Tracey Gibson Mark Dowton

Publish Date: 2008/02/21

Volume: 66, Issue: 3, Pages: 197-209

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Abstract

We sequenced a mitochondrial subgenome from the nematode Globodera rostochiensis in two overlapping pieces The subgenome was 9210 bp and contained four proteincoding genes ND4 COIII ND3 Cytb and two tRNA genes tRNA Thr tRNA Gln Genome organization was similar to that of Globodera pallida which is multipartite Together with the small number of genes on this subgenome this suggests that the mitochondrial genome of G rostochiensis is also multipartite In the initial clones sequenced COIII and ND3 were fulllength while ND4 and Cytb were interrupted by premature stop codons and contained point indels that disrupted the reading frame However sequencing of multiple clones from DNA extracted both from multiple individuals and from single cysts revealed a predominant source of variation—in the length of polythymidine tracts Comparison of our genomic sequences with ESTs similarly revealed variation in the length of polythymidine tracts We subsequently sequenced both genomic DNA and mRNA from populations of G pallida In each case variation in the length of polythymidine tracts was observed The levels of expression of mitochondrial genes in G pallida were representative of the subgenomes present little evidence of differential expression was observed These observations are consistent with the operation of posttranscriptional editing in Globodera mitochondria although this is difficult to show conclusively in the presence of intraindividual gene sequence variation Further alternative explanations cannot be discounted these include the operation of slippage during translation or that genomic copies of most genes are pseudogenes with a small proportion of fulllength sequences able to maintain mitochondrial functionThe authors thank Vincent Dubois who helped out with the sequencing of the G pallida material This work was funded by grants from the Australian Research Council the Scottish Executive Environment and Rural Affairs Department and EU AIR3 CT92–0062

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