SECRETION OF HUMAN INTERLEUKIN-2 IN BIOLOGICALLY-ACTIVE FORM BY BACILLUS-BREVIS DIRECTLY INTO CULTUTE MEDIUM

We constructed an efficient system for synthesis and secretion of huma n interleukin-2 (IL-2) by Bacillus brevis. The secretion vector we con structed had strong promoters and contained the region coding for the signal peptide of the gene for B. brevis 47 cell-wall protein, followe d directly by the gene encoding mature IL-2. Modification of the signa l peptide and use of a protease-deficient mutant of B. brevis HPD31 in creased productivity. When the signal peptide was more basic near its amino terminal and more hydrophobic in the middle region, IL-2 product ion increased 20 fold. Production by the mutant harboring the secretio n vector was four fold that of the parent harboring the same plasmid. The yield of IL-2 increased further to 0.12 g/liter, when cultural con ditions were made optimal, such by the addition of Tween 40 to the med ium. The IL-2 produced by B. brevis had the same biological activity a s authentic IL-2. Biologically active human IL-2 was produced efficien tly and secreted directly into the medium by B. brevis.