The insertional mutagen thus allows identification of one or more genes that are mutated by insertion of an insertional mutagen.

The mutation of M.bovis-BCG, M.tuberculosis, or M.leprae is preferably effected through an insertional mutation of a mycobacterial gene.

Next, the nucleic acid sequence of each exon found to contain an insertion or deletion mutation is determined, or of all exons in the event no insertion or deletion mutations are identified.

Another gene for polysaccharide biosynthesis, designated gell in gellan producing strains, was inactivated by insertion mutation and also shown to produce the slime phenotype.

Differences in length between an amplified sample exon and the corresponding amplified wild-type exon reflect the occurrence on an insertion or deletion mutation in the sample RB1 gene.