Colony probing as an alternative to standard sequencing as a means of direct analysis of chromosomal DNA to determine the spectrum of single-base changes in regions of known sequence.

We demonstrate here the means to directly analyze bacterial chromosomal DNA for all classes of single-base mutations in a specific codon in any region of known sequence through the use of DNA probing as a powerful substitute for standard sequencing techniques. With this method, chromosomal DNA from hundreds of mutants can be examined for single-base changes without any DNA cloning. This method can conveniently provide a large data base for the assessment of all classes of single-base mutations occurring spontaneously or induced by a known or suspected mutagen. The method is demonstrated for the analysis of histidine-independent (His+) revertants of hisG46, a missense mutation of Salmonella typhimurium that can revert in six or seven ways.