Cloning and sequence analysis of the β2-microglobulin transcript from flounder, Paralichthys olivaceous

beta(2)-Microglobulin (beta M-2) is a protein found free-form in the serum or on the cell surface non-covalently associated with the alpha-chain of the class I major histocompatibility (MHC-1) complex. The full-length cDNA containing beta M-2 was cloned from flounder. Paralichthys olivaceous. The transcript consists of 1610 nucleotides (nts), including an open reading frame (ORF) of 384 nts encoding a polypeptide of 128 amino acids. The amino acid sequence of beta M-2 in flounder is 59, 57, 56, and 48% conserved in catfish, rainbow trout, zebrafish, and humans, respectively. Genomic Southern hybridization suggested the presence of a single copy of beta M-2 in the flounder genome, and reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis detected the beta M-2 transcript in the head kidney, spleen, body kidney, liver, and muscle tissues of the flounder. PCR amplification and sequence analysis revealed the lack of ail intron in the beta M-2 gene. The phylogenetic analysis confirmed the evolutionary diversion of the beta M-2 protein among warm-blooded vertebrates and fish, and the separation between freshwater and seawater fish. (c) 2005 Elsevier Ltd. All rights reserved.