TABLE 1.

Type III secretion and targeting of Y. enterocolitica strains W22703 and LC7 during the infection of cultured HeLa cells^a

Type III export substrate	Y. enterocoliticaW22703 (wild type)		Y. enterocolitica LC7 (tyeA2)
	Digitonin extracted (%)b	Secreted (%)c	Digitonin extracted (%)	Secreted (%)
YopE	71	3	24	27
YopN	64	0	68	27
YopM	90	7	30	52
YopH	62	6	19	54

^aTissue flasks with confluent HeLa cell cultures were infected with Yersinia strains for 3 h. The medium was decanted and centrifuged to separate the extracellular medium from the bacterial sediment. HeLa cells were extracted with digitonin and centrifuged to separate the soluble cytosolic contents from the sediment of bacteria adhering to the plasma membrane. Protein in all fractions was precipitated with chloroform-methanol and analyzed by immunoblotting (see Fig. 2). 

^bAmount of immunoreactive polypeptide in the supernatant of centrifuged tissue culture medium divided by the total amount present in all fractions (medium supernatant and pellet as well as digitonin extract supernatant and pellet). 

^cAmount of immunoreactive polypeptide in the supernatant of digitonin extracts divided by the total amount present in all fractions (media supernatant and pellet as well as digitonin extract supernatant and pellet).