Abstract: Plasmid vectors are provided that carry complementary DNA (cDNA) clones cng for polypeptides exhibiting murine interleukin-2 activity. One of these polypeptides is 168 amino acids in length, including a potential leader sequence of about 19 amino acids. The cDNA is derived from messenger RNA isolated from a mouse T-cell line after activation with concanavalin A. The cDNA was cloned by incorporation into a plasmid vector, which is then transformed into E. coli. The plasmid vector also contained DNA segments from the SV40 virus, permitting expression of the cDNA after transfection into a mammalian host cell, such as monkey COS-7 cells.