Final answer:
Insertion Sequences (IS Elements) are stretches of DNA within bacterial genomes or plasmids that have the ability to move from one location to another in the DNA. They contain genes for enzymes needed for this mobility and are bounded by inverted repeats. Because of the limited non-coding DNA in bacteria, only a few IS elements are present to avoid harmful mutations.
Step-by-step explanation:
Insertion Sequences in Bacterial Mobile Genetic Elements
Insertion Sequences (IS Elements) are a type of bacterial mobile genetic elements that were some of the first to be described after those found in maize. IS elements consist of a stretch of DNA that ranges in length from about 750 to 1425 base pairs (bp) and contain genes for transposase and resolvase, which are enzymes required for their mobility. These elements are characterized by inverted repeats at either end and are flanked by direct repeats of the host genome or plasmid DNA, which arise as a result of the transposition process.
Bacteria's compact genomes can only tolerate a limited number of IS elements since there is less non-coding DNA to buffer against potentially damaging mutations incurred by transposition events. Therefore, bacteria typically harbor low copy numbers of IS elements, which may be as few as one or less than ten. These IS elements are largely silent in nature but can be experimentally induced to transpose in laboratory settings.
When IS elements lie close to each other and are separated by a short stretch of DNA, they may transpose together as part of a composite transposon, known as a Tn element, which potentially carries additional genes, such as antibiotic resistance genes.