FIG. 1.
(a) PCR test to demonstrate the absence of residual contaminating 16S rDNA in DNase-treated mRNA samples. E. coli cells (107 cells/ml) were heat inactivated at 100°C for 5 min and then left at room temperature for 16 h (lane 2) after the killing treatment. Lane 1 contains an unheated control sample, lane 3 is a negative control containing sterile water in place of nucleic acid, and lane 4 is a positive control containing E. coli DNA. Lanes M contain molecular size standards. (b) Southern blot analysis of PCR products from amplification of residual contaminating 16S rDNA in DNase-treated mRNA samples. The gel in panel a was blotted and probed with a fluorescein-labelled 16S rDNA fragment.