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Although we now have in hand a functional Xf PG enzymatic activity assay we would still like to obtain greater amounts of active Xf PG. The first attempt at using a recently developed agroinfection-compatible tobacco mosaic virus protein expression system (Lindbow, 2007) did not provide us with active Xf PG. However, we produced two new Xf PG plant expression constructs that might improve our Xf PG yields using the plant expression system. The first involves changing the structure of the gene near the start codon to make it more conducive to use in plant expression systems. The second employs the use of a Rice Alpha Amylase signal peptide that will export Xf PG to plastids and extracellular compartments (Chen, et al., 2004). Targeting the Xf PG to these organelles could be important if the reason we are not getting active Xf PG is because the plant is recognizing it and degrading it in the cytoplasm. In addition to the plant expression system we are currently using to create a greater amount of active Xf PG, we are also generating constructs for E. coli expression systems that fuse Xf PG to Maltose Binding Protein (MBP) in the hopes the MBP will help overcome some of the insolubility issues we have encountered with previous bacterial fusion protein expression systems. The method we described in the previous reporting period for generating active Xf PG remains the method that delivers the most protein in active form, however we hope that one of these new strategies will provide us with an even greater amount of active protein. As was reported in the previous period we feel confident that the reducing sugar assays that we are using to detect Xf PG activity, dinitrosalicylic acid (Fig. 1) (Wang et al., 1997) and 3-Methyl-2-benzothiazolinonehydrazone methods (Anthon and Barrett 2002) will be suitable for the PG-inhibition assays.