| A set of F ' strains of Escherichia coli K 12 partially diploid for various chromosomal segments has been examined for possible gene dosage effects in the synthesis of sigma factor of the DNA dependent RNA polymerase ( RNA nucleotidyltransferase ; nucleoside triphosphate : RNA nucleoti dyltransferase , EC 2 . 7 . 7 . 6 ) . ^^^ |