Molecular cloning of gerbil interleukin 12 and its expression as a bioactive single-chain protein

Complementary DNAs coding for gerbil interleukin 12 (IL-12) p40/p35 subunits were cloned by a combination of cross species reverse transcriptase-polymerase chain reaction (RT-PCR) and 3' rapid amplification of cDNA ends (RACE) techniques. IL-12 p40/p35 had 79% nucleotide identity and 81% amino acid homology to mouse IL-12 p40/p35. The p40/p35 subunits were expressed as a single polypeptide separated by a short hinge sequence that allowed for proper folding and assembly. COS-7 cells transfected with DNA encoding the single-chain gerbil IL-12 (pSCjIL12) secreted high levels of the protein which stimulated proliferation of ConA-activated gerbil spleen lymphoblasts in a dose-dependent manner.