Toung Y P, Hsieh T S, Tu C P
Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802.
J Biol Chem. 1993 May 5;268(13):9737-46.
We have characterized a cluster of glutathione S-transferase genes located at 87B on the Drosophila polytene chromosome near the heat shock genes, hsp70. These genes, designated gst Ds in the glutathione S-transferase gene superfamily, are closely linked within a approximately 60-kilobase DNA segment. The gene family has a minimum of eight intronless genes organized in divergent orientations. Two of the genes are probably GST pseudogenes in that their open reading frames are shorter than functional GSTs, and no RNAs from them have been detected thus far. The amino acid sequence identity among the functional genes ranges from 53 to 75% in pairwise comparisons. The intergenic regions are much more AT rich (63-73%) than the coding regions (41-52%), consistent with being promoter/regulatory sequences in Drosophila melanogaster. The mRNA size for each gene suggests that these genes are probably expressed individually from separate promoters. This is the first documentation of definitive physical linkage of a functional glutathione S-transferase multigene family. The genes are divergently organized, and a gradation of sequence similarity exists among the encoded GST isozymes. The patterns of sequence similarity in pairwise comparisons of the family members suggest that gene conversion may have played a role in the evolution of this GST multigene family. We propose that the Drosophila gst D genes provide a unique system for studying GST gene regulation, in vivo physiological functions, and evolution of substrate specificities with a global perspective. The gst D genes in other organisms should be intronless and can be isolated directly from genomic DNAs for functional analyses at the gene and protein levels.
我们已经对位于果蝇多线染色体87B处、靠近热休克基因hsp70的一组谷胱甘肽S-转移酶基因进行了表征。在谷胱甘肽S-转移酶基因超家族中，这些被命名为gst Ds的基因在一个约60千碱基的DNA片段内紧密连锁。该基因家族至少有八个无内含子基因，以不同方向排列。其中两个基因可能是谷胱甘肽S-转移酶假基因，因为它们的开放阅读框比功能性谷胱甘肽S-转移酶短，且迄今为止尚未检测到来自它们的RNA。在成对比较中，功能性基因之间的氨基酸序列同一性范围为53%至75%。基因间区域比编码区域富含更多的AT（63%-73%），这与黑腹果蝇中的启动子/调控序列一致。每个基因的mRNA大小表明这些基因可能从单独的启动子单独表达。这是功能性谷胱甘肽S-转移酶多基因家族明确物理连锁的首次记录。这些基因呈发散性排列，编码的谷胱甘肽S-转移酶同工酶之间存在序列相似性梯度。家族成员成对比较中的序列相似性模式表明基因转换可能在这个谷胱甘肽S-转移酶多基因家族的进化中发挥了作用。我们提出果蝇gst D基因提供了一个独特的系统，用于从全局角度研究谷胱甘肽S-转移酶基因调控、体内生理功能以及底物特异性的进化。其他生物体中的gst D基因应该是无内含子的，可以直接从基因组DNA中分离出来进行基因和蛋白质水平的功能分析。
