Arabidopsis thaliana possesses two isoforms of plastidic ATP/ADP transporters (AtNTT1 and AtNTT2), which have similar biochemical characteristics. Using AtNTT1-2::T-DNA and RNAi mutants, the physiological role of these transporters in plastid energy metabolism could be documented. In addition to the two NTT isoforms, Arabidopsis thaliana possesses the genetic information for a further putative nucleotide transporter (AtNTT3).

The search for the coding sequence revealed that the corresponding mRNA is present in a large number of splice variants never before described for transport proteins. A complete survey of the variants in different tissues and under different environmental conditions is currently being carried out.

The amino acid sequence of AtNTT3 is very similar to a bacterial NAD transporter from Protochlamydia amoebophila. Since AtNTT3 does not have an N-terminal sequence extension with a plastidic target signal, it can be assumed that this transporter - unlike all other plant NTTs - is not localized in plastids. Ultimately, investigations with the AtNTT3-GFP fusion protein will provide information on the cellular localization of AtNTT3. The function of the corresponding transporter and its role in plant metabolism can so far only be speculated upon. Therefore, the focus is on determining the biochemical properties of this novel transporter.