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Title: NAT2/AAP1 AS A PROTOTYPICAL EXAMPLE OF THE AAP AMINO ACID SYMPORTER GENE FAMILY: FROM PROTEIN TOPOLOGY TO REGULATION OF GENE EXPRESSION

Author
item CHANG, HUI-CHU - PLANT BIOLOGY UOFI URBANA
item BUSH, DANIEL

Submitted to: Journal of Experimental Biology Online, Vol 3
Publication Type: Abstract Only
Publication Acceptance Date: 8/14/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Amino acids are the predominant form of nitrogen available to the heterotrophic tissues of plants. In the results reported here, we determined the topology of NAT2 in the membrane and we identified several factors that control its expression in the plant. Engineered proteins with a c-myc epitope on either the N- or C-terminus of NAT2 were used to determine its topology by in vitro translation, partial digestion with proteinase K, and immunoprecipitation to identify a group of oriented-peptide fragments. Based on the combined data, we propose a novel 11 transmembrane domain model with the N-terminus in the cytoplasm and C-terminus facing outside the cell. We have also examined the regulation of NAT2/AAP1 expression in the plant. The message of NAT2 is detected in the leaves, cauline leaves, flowers and green pods. We have isolated the genomic clone of NAT2 from an Arabidopsis genomic DNA library. The nucleotide sequence of NAT2 promoter contains several motifs that are putatively involved in nitrogen metabolism. Significantly, we show here that NAT2 expression is nitrate and light inducible, but not circadian-regulated. Since the nitrate assimilatory enzymes are also induced by nitrate, the nitrate-inducible expression of NAT2 provides good evidence connecting nitrate assimilation and amino acid transport. This observation supports the notion that NAT2 may be involved in phloem loading of newly synthesized amino acids in leaves.