Loguercio L L, Wilkins T A
Department of Agronomy and Range Science, University of California, One Shields Avenue, Davis, CA 915616-8515, USA.
Curr Genet. 1998 Oct;34(4):241-9. doi: 10.1007/s002940050393.
Structural analysis of hmg-coA reductase (hmgr) genes in the allotetraploid cotton species Gossypium hirsutum L. revealed the first-known existence of a pseudogene, psihmg5, for this important enzyme. Complete sequencing of the genomic clone hmg5 unveiled several deleterious lesions, resulting in an organization that departed significantly from the linear canonical hmgr gene structure. Although analysis of the 5' flanking region indicated a promoter-like composition based on comparison with other known plant hmgr genes, the precise loss of intron 3, and putative poly-(A) signals, small poly-(A) tracts, and terminal repeats (TRs) found in the 3'-flanking region are characteristic features of retro-pseudogenes. DNA-blot analysis indicated that a psihmg5-related subfamily exists within a larger hmgr gene family in cotton. Several mechanisms are proposed to account for the formation of this partially intronless pseudogene, including intragenic homologous-replacement recombination and gene conversion involving a cDNA. Alignments of psihmg5 with functional cotton homologs also raised interesting possibilities for the formation of 'chimeric' gene structures, or differential intragenic mutation rates, as potential evolutionary mechanisms involved in shaping the hmgr gene family in cotton.
对异源四倍体棉花物种陆地棉（Gossypium hirsutum L.）中HMG-CoA还原酶（HMGR）基因的结构分析揭示了该重要酶的首个已知假基因psihmg5的存在。基因组克隆hmg5的完整测序揭示了几个有害损伤，导致其结构与线性经典HMGR基因结构有显著差异。虽然对5'侧翼区域的分析表明，与其他已知植物HMGR基因相比，其具有类似启动子的组成，但内含子3的精确缺失，以及在3'侧翼区域发现的推定聚腺苷酸信号、小聚腺苷酸片段和末端重复序列（TRs）是反转录假基因的特征。DNA印迹分析表明，在棉花更大的HMGR基因家族中存在一个与psihmg5相关的亚家族。提出了几种机制来解释这个部分无内含子假基因的形成，包括基因内同源替换重组和涉及cDNA的基因转换。psihmg5与功能性棉花同源物的比对也为“嵌合”基因结构的形成或不同的基因内突变率提出了有趣的可能性，作为塑造棉花HMGR基因家族的潜在进化机制。
