Some properties of the ribosomal RNA methyltransferase encoded by ksgA and the polarity of ksgA transcription.

The assay for the ksgA-encoded S-adenosylmethionine--6-N',N'-adenosyl (rRNA) dimethyltransferase has been improved; the gel-filtration molecular weight of partially purified enzyme under two different sets of conditions was found to be 55,000 or 26,000 daltons. We have determined methyltransferase activities in strains where ksgA was brought under the control of the mitomycin C-inducible promoter of the colicin E1 gene. Our studies show that ksgA is transcribed counterclockwise on the Escherichia coli chromosome.