IG HEAVY-CHAIN OF THE STURGEON ACIPENSER BAERI - CDNA SEQUENCE AND DIVERSITY

To investigate the gene organization of the ICH locus, and the VH dive rsity of the Siberian sturgeon, a cDNA library was constructed and scr eened with VH-specific probes from two holostean fish. Isolated clones were analyzed and domain-specific probes used in rescreening of the l ibrary, Southern blot analysis, and northern blots. It was concluded t hat the Siberian sturgeon has one IGH locus with a translocon type of organization. Two allelic variants of the mu gene were found, with ide ntities ranging from 80 to 100% for the different domains (highest for CH4 and lowest for CH2). Sturgeon CH sequences are most closely relat ed to those of holostean fish. There are three distinct VH families, V HI grouping with mammalian dan III, VHII grouping with the teleost dan , and VHIII grouping with the archaic dan. The variability of the CDR 3 region is substantial, and we identified a number of conserved motif s in the D segment. Further, we deduced that there are at least nine d ifferent JH segments in the locus, contributing to the antibody repert oire of the sturgeon. The variable segments of the three families can be associated with any of the D or JH segments in the rearrangement. S turgeon, in addition to the random rearrangement of VH, D, and JH segm ents, have exonuclease activity, and an introduction of N and probably P nucleotides at the site of rearrangement.