FORMATION OF ICE NUCLEATION-ACTIVE VESICLES IN ERWINIA-UREDOVORA AT LOW-TEMPERATURE AND TRANSPORT OF INAU MOLECULES INTO SHED VESICLES

An ice nucleation-active strain of Erwinia uredovora shed vesicles whe n cultured at low temperature (10 degrees C). We isolated an ice nucle ation-active vesicle fraction from the culture medium by ultrafiltrati on, ultracentrifugation, and gel filtration. Western blot analysis sho wed that this cell-free vesicle fraction contained an ice nucleation-a ctive protein (InaU), The process of the InaU transport to a shed vesi cle was examined by immunohistochemical analysis using electron micros copy, The examination showed the following successive processes: InaU molecules first assemble around the inner membrane, then the assembly enters a vesicle just forming on the surface of the outer membrane, an d finally the vesicle, 100-400 nm in diameter, leaves the surface to b e shed with InaU molecules occluded.