Abstract: Transcriptional activator protein（AhyR）gene of Aeromonas hydrophila strain Zf1 was amplified by PCR using the designed primers, resulting in a 1 063 bp DNA sequence. The sequencing analyses revealed AhyR gene encoding a protein of 260 amino acids which has autoinducer binding domain（18-168 aa）and LuxR-type helix-turn-helix（HTH）domain for DNA binding（176-241 aa）. Moreover, AhyR protein was predicted containing 13 phosphorylation sites（ie., 15S, 30T, 62S, 144S, 145S, 156S, 161Y, 173S, 184T, 188T, 200S, 227S and 231Y）. The homology modeling of 3D structure of AhyR protein was carried out based on the template retrieved from chain A of quorum sensing control repressor（PDB：3SZT_A）. AhyR protein showed the homology of 28.40% with the standard model, and the physiological activity subunit LuxR-type HTH domain profile was located in the outer surface of the C-terminal. The quality of the resulting protein structure was further checked by the Ramachandran plot.

Key words: Aeromonas hydrophila, Transcriptional activator protein, Sequence analysis, 3D structure