Nemer M, Thornton R D, Stuebing E W, Harlow P
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
J Biol Chem. 1991 Apr 5;266(10):6586-93.
The metallothionein-B genes of the sea urchin Strongylocentrotus purpuratus encode a metallothionein (MT) isoform distinguishable from the MTA isoform. The MTB subfamily consists of at least two genes, MTB1 and MTB2, and possibly two to three others. The unique MTB1 and MTA genes have a high degree of identity but diverge in structural detail and expression. Transcripts of the MTA, MTB1, troponin C Spec 1, and CyIIIa actin genes begin simultaneously to accumulate at an early blastula stage. MTB1 mRNA becomes localized in the embryonic gut and oral ectoderm, whereas MTA, Spec 1, and CyIIIa actin mRNAs are spatially restricted to the aboral ectoderm. Several DNA elements are localized at the same positions in the MTB1 and MTA genes: these include respective CATA and TATA boxes, two metal response elements, and three distinct upstream DNA elements that are also present, and in the same order, in the Spec 1 gene promoter. A heptameric sequence, element A, is present at two sites each in the Spec 1 and CyIIIa actin genes, five sites in MTA, but only one site in MTB1. Most strikingly, the first intron of MTA contains elements not found in the MTB1 introns, including a consensus metal response element, an element A, and the P3A site demonstrated in the CyIIIa actin gene to be linked to the regulation of spatial expression.
紫海胆（Strongylocentrotus purpuratus）的金属硫蛋白-B基因编码一种与MTA亚型不同的金属硫蛋白（MT）亚型。MTB亚家族至少由两个基因MTB1和MTB2组成，可能还有另外两到三个基因。独特的MTB1和MTA基因具有高度的同一性，但在结构细节和表达上存在差异。MTA、MTB1、肌钙蛋白C Spec 1和CyIIIa肌动蛋白基因的转录本在囊胚早期开始同时积累。MTB1 mRNA定位于胚胎肠道和口外胚层，而MTA、Spec 1和CyIIIa肌动蛋白mRNA在空间上局限于反口外胚层。几个DNA元件位于MTB1和MTA基因的相同位置：这些元件包括各自的CATA和TATA框、两个金属反应元件以及三个不同的上游DNA元件，它们也以相同的顺序存在于Spec 1基因启动子中。一个七聚体序列元件A在Spec 1和CyIIIa肌动蛋白基因中各有两个位点，在MTA中有五个位点，但在MTB1中只有一个位点。最引人注目的是，MTA的第一个内含子包含MTB1内含子中未发现的元件，包括一个共有金属反应元件、一个元件A以及在CyIIIa肌动蛋白基因中显示与空间表达调控相关的P3A位点。
