Gupta A, Morby A P, Turner J S, Whitton B A, Robinson N J
Department of Biological Sciences, University of Durham, UK.
Mol Microbiol. 1993 Jan;7(2):189-95. doi: 10.1111/j.1365-2958.1993.tb01110.x.
Genomic rearrangements involving amplification of metallothionein (MT) genes have been reported in metal-tolerant eukaryotes. Similarly, we have recently observed amplification and rearrangement of a prokaryotic MT locus, smt, in cells of Synechococcus PCC 6301 selected for Cd tolerance. Following the characterization of this locus, the altered smt region has now been isolated from a Cd-tolerant cell line, C3.2, and its nucleotide sequence determined. This has identified a deletion within smtB, which encodes a trans-acting repressor of smt transcription. Two identical palindromic octanucleotides (5'-GCGATC-GC-3') traverse both borders of the excised element. This palindromic sequence is highly represented in the smt locus (7 occurrences in 1326 nucleotides) and analysis of the GenBank/EMBL/DDBJ DNA Nucleotide Sequence Data Libraries reveals that this is a highly iterated palindrome (HIP1) in other known sequences from Synechococcus strains (estimated to occur at an average frequency of once every c. 664 bp). HIP1 is also abundant in the genomes of other cyanobacteria. The functional significance of smtB deletion and the possible role of HIP1 in genome plasticity and adaptation in cyanobacteria are discussed.
在耐金属的真核生物中，已报道了涉及金属硫蛋白（MT）基因扩增的基因组重排。同样，我们最近在因耐镉而筛选出的聚球藻PCC 6301细胞中观察到一个原核MT基因座smt的扩增和重排。在对该基因座进行表征之后，现已从耐镉细胞系C3.2中分离出改变后的smt区域，并确定了其核苷酸序列。这确定了smtB内的一个缺失，smtB编码smt转录的反式作用阻遏物。两个相同的回文八聚体（5'-GCGATC-GC-3'）横跨切除元件的两个边界。这个回文序列在smt基因座中高度富集（在1326个核苷酸中有7次出现），并且对GenBank/EMBL/DDBJ DNA核苷酸序列数据库的分析表明，这是来自聚球藻菌株的其他已知序列中的一个高度重复回文序列（HIP1）（估计平均每约664 bp出现一次）。HIP1在其他蓝细菌的基因组中也很丰富。本文讨论了smtB缺失的功能意义以及HIP1在蓝细菌基因组可塑性和适应性中的可能作用。
