Sucrose density gradient profiles and in vitro time course KsgA methylation assay of 30S subunit substrates. (A) Sucrose gradient profile of 30S subunits isolated from MRE600 E. coli strain made kasugamycin resistant (30SUnTag,UM) (B) Sucrose gradient analysis to determine the structural integrity of 30S subunits isolated from kasugamycin resistant DH5α strain expressing MS2 tagged 16S rRNA (30STag,UM). (C) The three curves are time courses of KsgA transferring tritiated methyl groups from S-adenosyl-L-methionine to three types of 30S subunits. Blue Diamonds: 30SUnTag,UM. Red Squares: 30STag,UM. Green Triangles: Same as Red Squares, but from a strain sensitive to kasugamycin, therefore natively methylated at A1518 and A1519 (30STag).