Cloning, characterization and genomic structure of the natural killer cell enhancement factor (NKEF)-like gene from homozygous clones of rainbow trout (Oncorhynchus mykiss)

Natural killer cell enhancement factor (NKEF) belongs to the antioxidant protein family. In the human, NKEF has the ability to enhance natural killer cell cytotoxic activity in vitro. In the present work, the cDNAs of NKEF from three strains of homozygous clones of rainbow trout were cloned from the splenic cDNA library of one of the strains, OSU142, and then by RT-PCR for the Hot Creek (HC) and Arlee (AR) strains. The HC sequence has 99% sequence identity with both OSU142 and AR. OSU142 and AR have only one nucleotide difference in the cDNA sequence. All three sequences have the same deduced NKEF peptide, which contains 199 amino acids. The 6. 5 kb genomic DNA of OSU142 containing NKEF was sequenced and contains six exons and five introns. Tissue specific expression of NKEF was studied by RT-PCR in eight different tissues of OSU142 and revealed that all tissues expressed NKEF. A southern blot revealed that the gene for NKEF is present in a single copy. The cDNA and amino acid sequences of trout NKEF have high similarity with human, rat, mouse and carp sequences, therefore, indicating that NKEF is a very conserved gene.