Insertion sequences(IS) -Insertion sequences are transposable genetic- elements that carry no known genes except those that are required for transposition a Nomenclature- Insertion sequences are given the designation IS followed by a number. e.g. IS1 b Structure Insertion sequences are small stretches of DNA that have at their ends repeated sequences, which are involved in transposition. In between the terminal repeated sequences there are genes involved in transposition and sequences that can control the expression of the genes but no other nonessential genes are present c, Importance 2-1 Mutation-The introduction of an insertion sequence into a bacterial gene wil result in the inactivation of the gene Hi) Plasmid insertion into chromosomes- The sites at which plasmids insert into the bacterial chromosome are at or near insertion sequence in the chromosome Phase Variation- The flagellar antigens are one of the main antigens to which the immune response is directed in our attempt to fight off a bacterial infection In salmonella there are two genes which code for two antigenically different flagellar antigens. The expression of these genes is regulated by an insertion sequences. In one orientation one of the genes is active while in the other orientation the other flagellar gene is active. Thus, Salmonella can change their flagella in response to the immune systems' attac Phase variation is not unique to Salmonella flagellar antigens. It is also seen with other bacterial surface gens. Also the mechanism of phase variation may differ in different species of bacteria(e. g Neisseria transformation) ABCDEFG Transposase GFEDCRAInsertion sequences (IS)- Insertion sequences are transposable genetic elements that carry no known genes except those that are required for transposition. • a. Nomenclature - Insertion sequences are given the designation IS followed by a number. e.g. IS1 • b. Structure Insertion sequences are small stretches of DNA that have at their ends repeated sequences, which are involved in transposition. In between the terminal repeated sequences there are genes involved in transposition and sequences that can control the expression of the genes but no other nonessential genes are present. • c. Importance • i) Mutation - The introduction of an insertion sequence into a bacterial gene will result in the inactivation of the gene. • ii) Plasmid insertion into chromosomes - The sites at which plasmids insert into the bacterial chromosome are at or near insertion sequence in the chromosome. • iii) Phase Variation - The flagellar antigens are one of the main antigens to which the immune response is directed in our attempt to fight off a bacterial infection. In Salmonella there are two genes which code for two antigenically different flagellar antigens. The expression of these genes is regulated by an insertion sequences. In one orientation one of the genes is active while in the other orientation the other flagellar gene is active. Thus, Salmonella can change their flagella in response to the immune systems' attack. Phase variation is not unique to Salmonella flagellar antigens. It is also seen with other bacterial surface antigens. Also the mechanism of phase variation may differ in different species of bacteria (e.g. Neisseria; transformation)