Insertion of an artificial intron does not rescue expression of gH and gL. Intron1 of the human beta-globin gene was inserted into the coding regions of c.o. gH, gH, c.o. gL, and gL, and protein expression from the resulting constructs (c.o. gH-I and gH-I [A], c.o. gL-I and gL-I [B]) were measured together with the expression from the parental constructs in HEK293T cells at 36 h posttransfection by immunoblotting.