The open reading frame 1883 of the phytopathogen Xanthomonas citri's main chromosome is adjacent to the rpf locus that controls quorum sensing in Xanthomonas. It codes for an 82-residue protein of unknown function, XAC1883, containing a SpoVT/AbrB domain (Pfam family 04014) in its amino terminus (residues 3-48). The best characterized member of this family, AbrB from Bacillus subtilis, is a DNA binding protein known to control the transcription of genes involved in the control of stationary phase functions and sporulation. Therefore, in Xanthomonas, XAC1883 could be a transcription regulator that acts on promoters of genes involved in quorum sensing pathways. In order to gain insight into XAC1883 function, we are studying its solution structure by high resolution NMR. Backbone resonance assignments are being carried out using standard triple resonance NMR experiments combined with the analysis of ¹⁵N edited TOCSY and NOESY spectra acquired with ¹⁵N labeled and ¹³C/¹⁵N doubly labeled samples. As much as 88 % of the backbone resonances were assigned. Residues Glu⁷, Gln¹¹ and Lys⁵⁴-Val⁵⁸ are not yet assigned as their H^N cross peaks are missing in the ¹⁵N HSQC spectrum possibly due to exchange broadening. The resonances of Ala⁶, Arg⁸ and Gly⁹ are only observable at higher temperature (35 ⁰C), suggesting that part of the N-terminal segment of the protein undergoes conformational exchange at the NMR time scale. Nevertheless, secondary structure predictions based on chemical shifts indicate the presence of two short beta-strands at the N-terminus (residues 2 - 6 and 11 - 13), followed by an alpha-helix (residues 15 to 21), two more other beta-strands (residues 23-29 and residues 36-42) and a short helical segment between residues 46-49, while the C-terminal portion, residues 50-82 is predicted to be unstructured. These predictions were confirmed by the analysis of short range H^N-H^N and H^N-H^a NOEs which are indicative of beta-sheet or alpha-helix conformations. Experiments to test whether XAC1883 binds to specific promoter DNA sequences are being initiated.