Translocation of murine interleukin 2 into microsomes during translation in a cell-free system

Interleukin 2 (IL2) is a lymphokine which stimulates the growth of T lymphocytes. Although IL2 mRNA is translated into biologically active IL2 relatively efficiently in microinjected Xenopus laevis oocytes, it has been difficult to establish reproducible cell-free translation systems for this lymphokine. Such systems would be useful for the analysis of translational and post-translational events. In this paper, we show that a wheat germ extract will translate IL2 mRNA into biologically active murine IL2, most of which is translocated into dog pancreas microsomes when these are present. Translocation occurs only during translation, but wheat germ extracts translate IL2 mRNA whether microsomes are present or not. Surprisingly, reticulocyte lysates do not readily translate IL2 mRNA, and strongly inhibit its translation in wheat germ extracts. This inhibition can be partially alleviated by adding dog pancreas microsomes to the system. The inhibition seen with reticulocyte lysate may be attributable to the action of the signal recognition particle, which binds nascent secretory proteins, and blocks their further translation in the absence of the docking protein present in microsomes.