Cloning, Structural Organization and Chromosomal Mapping of Rat Costimulatory Molecule 4‐1BBL

4‐1BBL (TNFSF9) is a member of the tumor necrosis factor (TNF) ligand superfamily, which is expressed on some activated antigen presenting cells and B cells. We isolated a rat cDNA clone encoding the rat homologue of the human 4‐1BBL (GenBank accession No. AY259541). The deduced rat 4‐1BBL protein, consisting of 308 amino acids with a molecular weight of 33,469 Da, was a typical type II transmembrane glycoprotein, the same as human and murine 4‐1BBL. “SDAA” in the cytoplasmic domain of rat 4‐1BBL was deduced to act as the phosphorylation site for casein kinase I (“SXXS” motif), which is present in the cytoplasmic domains of human and murine 4‐1BBL, and all other TNF ligand family members known to utilize reverse signaling. The two introns of 4‐1BBL were also cloned (GenBank accession No. AY332409). Rat 4‐1BBL is much more homologous with murine 4‐1BBL than with human 4‐1BBL, in both nucleotide and amino acid sequences. Rat 4‐1BBL was expressed in all tested tissues: brain, lung, colon, liver, thymus, testicle, kidney, adrenal, stomach, spleen and heart. The chromosomal location of rat 4‐1BBL was first identified by bioinformatics, then by fluorescence in situ hybridization at 9q11 (GenBank accession UniGene No. Rn.46783). Rat, murine and human 4‐1BBL genes are evolved from a common gene. The identification and characterization of the rat counterpart of human 4‐1BBL will facilitate studies of the biological function of this molecule. Edited by Xiang‐Fu WU