Mobile elements and genome evolution

Mobile elements (MEs) are an important component of the genome in all eukaryotes and prokaryotes. MEs are divided into two large classes differing in the mechanism of transposition. Class I MEs are transposed via reverse transcription of their RNA transcripts. Class II MEs code for transposase, which acts at the DNA level and recognizes the ends of the cognate ME. The review considers the distribution of MEs from different classes in various genomes, individual chromosomes, and chromatin types. There is ample evidence for an important role of MEs in the regulation of cell genes and evolution of complex eukaryotic genomes. It is thought that ME invasion and subsequent amplification act as a main morphogenetic factor ensuring adaptation of populations to environmental changes and, in some cases, cause rapid speciation.