The nuclear protein factors which stimulate synthesis of mRNA of interleukin-2 (IL-2) in the system of surviving murine T lymphocytes are isolated from cells of the spleen and brain of immunized rats. The active fractions of spleen and brain (13-19 and 25 kD, respectively), which interact with the promoter-enhancer sequences of the IL-2 gene localized in the region from +39 to -141 base pairs, are isolated by the method of high performance liquid chromatography from the total nuclear extract. The induction of luciferase synthesis is shown for protein factor-treated Jurkat cells transformed with p-IL-2LUC recombinant plasmid.