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Background  The  Arabidopsis thaliana  genome encodes a homologue of the full-length bacteriophage T7 gp4 protein, which is also homologous to the eukaryotic Twinkle protein. While the phage protein has both DNA primase and DNA helicase activities, in animal cells Twinkle is localized to mitochondria and has only DNA helicase activity due to sequence changes in the DNA primase domain. However,  Arabidopsis  and other plant Twinkle homologues retain sequence homology for both functional domains of the phage protein. The  Arabidopsis  Twinkle homologue has been shown by others to be dual targeted to mitochondria and chloroplasts.    Results  To determine the functional activity of the  Arabidopsis  protein we obtained the gene for the full-length  Arabidopsis  protein and expressed it in bacteria. The purified protein was shown to have both DNA primase and DNA helicase activities. Western blot and qRT-PCR analysis indicated that the  Arabidopsis  gene is expressed most abundantly in young leaves and shoot apex tissue, as expected if this protein plays a role in organelle DNA replication. This expression is closely correlated with the expression of organelle-localized DNA polymerase in the same tissues. Homologues from other plant species show close similarity by phylogenetic analysis.    Conclusions  The results presented here indicate that the  Arabidopsis  phage T7 gp4/Twinkle homologue has both DNA primase and DNA helicase activities and may provide these functions for organelle DNA replication.

The ArabidopsisAt1g30680 gene encodes a homologue to the phage T7 gp4 protein that has both DNA primase and DNA helicase activities