CLONING, SEQUENCINGα1-MICROGLOBULIN/BULININPRECURSO cDNA OFGRASSCARP, CTENOPHARYNGODONIDELLUS

α1-Microglobulin and bikunin are both plasma proteins which are synthesized from a common mRNA with tandemly arranged coding sequence and their functions are unrelated.α1-Microglobulin is a glycoprotein that associates with other plasma proteins.α1-Microglobulin belongs to Lipocalin family,has immunoregulatory properties.Bikunin is a Kunitz-type proteinase inhibitor of the inter-α-inhibitor family.Complementary DNAs(cDNAs) of α1-microglobulin/Bulinin precursor(AMBP) encoding α1-microglobulin/bikunin,were cloned from liver extracts of grass carp,Ctenopharyngodon idellus,by reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends methods.The full-length α1-microglobulin/Bulinin precursor cDNA of grass carp consisted of a sequence of 1230 bp comprising a 23 bp 5'untranslated region(UTR),a 160 bp 3'-UTR and a 1047 bp open reading frame(ORF) encoding a 348 amino acid peptide.This included α1-microglobulin,182 amino acids,and bikunin,the light chain of the plasmaprotein inter-α-inhibitor,145 amino acids.The two proteins were connected by a basic tetrapeptide,R-A-R-R,which conformed to the consensus sequence recognized by endoproteolytic cleavage enzymes.Their part displayed sequence motifs typical for members of the lipocalin and Kunitz-type protease inhibitor superfamilies,respectively.The deduced amino acid sequence showed a high degree of identity with α1-microglobulin and bikunin sequences from other species,from 44.7% to 84.4%,in which the highest homology species were between grass carp and zebrafish(84.4%).These results suggested that the structure of the α1-microglobulin/bikunin mRNA was conserved in teleosts and other species,implying an important common function for the tandem expression of these proteins.