Chapter 42 : Control of Mobile DNA

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Transposons are almost invisible genetically. There are two reasons for this genetic invisibility. First, transposons and retrotransposons generally move at extremely low frequencies, and second, they participate in illegitimate recombination events at frequencies much lower than anticipated from homology. Transposons and retrotransposons comprise half or more of the maize genome. The major difference between the maize and sorghum regions is the presence of very large continuous blocks of retrotransposons in maize that are not present in sorghum. Importantly, no retrotransposons have been found in the corresponding flanking sequence in sorghum. Recent work in a wide variety of organisms has begun to reveal previously unsuspected, and often interconnected, mechanisms for monitoring both gene expression levels and gene redundancy. Moreover, it is becoming increasingly evident that such mechanisms are central to controlling the expression and transposition of mobile elements. The results of recent studies on the classical epigenetic phenomenon of R locus paramutation in maize have revealed that local endoreduplication of a chromosomal segment both triggers silencing and can render the endoreduplicated locus capable of silencing an active allele of the gene on a homolog. Although the successful constitution of a transposon from the recognition sequences used in immunoglobulin gene rearrangement and the RAG1 and RAG2 proteins was interpreted as evidence that the V(D)J recombination system evolved from an ancient mobile DNA element, the fact is that the critical components of a transposon and a site-specific rearrangement system are the same.

Citation: Fedoroff N. 2002. Control of Mobile DNA, p 997-1007. In Craig N, Craigie R, Gellert M, Lambowitz A (ed), Mobile DNA II. ASM Press, Washington, DC. doi: 10.1128/9781555817954.ch42
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