DNA was isolated from Russian sturgeon (Acipenser gueldenstaedii) tissue samples or individual caviar grains of Russian and Siberian sturgeon (A. baerii) from farms in Israel, North Carolina, and Florida. A repetitive 675 bp VAC-2M sequence identified in Russian sturgeon DNA aligns with the Siberian sturgeon IGLV gene cluster. A specific 218 bp long portion of the sequence was found to be identical between A. gueldenstaedtii, A. baerii and A. stellatus species and NCBI blast analysis confirmed the presence of the respective DNA segment in the A. ruthenus genome. Multiple mutated copies of the same genomic region were also detected by PCR analysis, indicating that different versions of this highly repetitive sequence exist simultaneously within the same organism. The process of selection toward specific mutation appears to be not random and is ongoing based on the sequence variations within DNA samples that derived from different individual caviar grains but originated from the same fish. The homologous between Russian and Siberian sturgeons 376 bp DNA fragment of the repetitive sequence was cloned either ahead or after the human cytomegalovirus immediate early promoter (HCMV-IE) into a pBV-Luc reporter vector expressing the luciferase gene. The DNA segment significantly reduced luciferase expression with maximum inhibition achieved when it was cloned in both orientations immediately after the HCMV-IE promoter (Figure 1). Thus, this genomic region functions as a transcription termination element. These results provide some new information about the role of
repetitive sequences within eucaryotic organisms in general and indicate that they may play
an important role in sturgeon immune system regulation.