this repression is concluded to be due to a cytoplasmic repressor since , when colb2 is present in cells containing an f factor ( either autonomous or integrated ) , f fertility is also repressed as shown by the inability of such ( colb2 ) ( + ) f ( + ) [ or ( colb2 ) ( + ) hfr ] strains to plaque f-specific phages , and by a reduction in the level of chromosomal transfer from such strains , compared to the corresponding f ( + ) ( or hfr ) control strains .
C0011389
plaque
C0016327
f