Ltr retrotransposons and the evolution of eukaryotic enhancers

Since LTR retrotransposons and retroviruses are especially prone to regional duplications and recombination events, these viral-like systems may be especially conducive to the evolution of closely spaced combinatorial regulatory motifs. Using the Drosophila copia LTR retrotransposon as a model, we show that a regulatory region contained within the element's untranslated leader region (ULR) consists of multiple copies of an 8 bp motif (TTGTGAAA) with similarity to the core sequence of the SV40 enhancer. Naturally occurring variation in the number of these motifs is correlated with the enhancer strength of the ULR. Our results indicate that inter-element selection may favor the evolution of more active enhancers within permissive genetic backgrounds. We propose that LTR retroelements and perhaps other retrotransposons constitute drive mechanisms for the evolution of eukaryotic enhancers which can be subsequently distributed throughout host genomes to play a role in regulatory evolution. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transposable elements and the evolution of genome size in eukaryotes

It is generally accepted that the wide variation in genome size observed among eukaryotic species is more closely correlated with the amount of repetitive DNA than with the number of coding genes. Major types of repetitive DNA include transposable elements, satellite DNAs, simple sequences and tandem repeats, but reliable estimates of the relative contributions of these various types to total genome size have been hard to obtain. With the advent of genome sequencing, such information is starting to become available, but no firm conclusions can yet be made from the limited data currently available. Here, the ways in which transposable elements contribute both directly and indirectly to genome size variation are explored. Limited evidence is provided to support the existence of an approximately linear relationship between total transposable element DNA and genome size. Copy numbers per family are low and globally constrained in small genomes, but vary widely in large genomes. Thus, the partial release of transposable element copy number constraints appears to be a major characteristic of large genomes.     

植物基因组中微型反向重复转座元件研究进展

微型反向重复转座元件(miniature inverted repeat transposable element,MITE)是一类特殊的转座元件,在结构上与有缺失的DNA转座子相似,但具有反转录转座子高拷贝数的特点.MITE时常与基因相伴,对基因调控可能起重要作用,因此,MITE正逐渐成为基因和基因组进化及生物多样性研究的一种重要工具.本文综述了植物基因组MITE的结构、分类、活性及其应用研究进展.