Analysis of activation of egr-1 and c-fos promoters through various hGMR mutants in BA/F3 cells. egr600CAT plasmid and c-fos-luciferase plasmid were transfected to BA/F3 cells expressing the wild-type hGMR;ga subunit and mutant ;gbc. Mutants of ;gb subunit are schematically shown in (A). CAT activities (▨) or luciferase activities (;bb) induced by hGM-CSF were analyzed as described in the Materials and Methods. (B) The C terminus truncated mutants from amino acid positions 455 to 763, or (C) internal deletions of either box1 or box2 of wild-type ;gbc or phenylalanine substitution of tyr577 of ;gb589 or wild-type ;gbc were used.