DNA was isolated from mycobacteria by a simplified procedure. Cells we
re suspended in 6 M guanidinium chloride, the suspension was cooled to
-70 degrees C, then incubated at 65 degrees C for 10 min, cooled in i
ce, deproteinized by chloroform and DNA was recovered from the superna
tant. The procedure was used to obtain DNA from several mycobacteria (
1 x 10(9) or more cells) including Mycobacterium neoaurum, M. fortuitu
m, M. phlei and M. smegmatis. Each of the species was shown to have tw
o ribosomal RNA operons per genome, and preliminary evidence was obtai
ned which suppests that one of these operons is homologous with one of
the operons of M. smegmatis.