The gal operon of Escherichia coli is negatively regulated by repressor binding to bipartite operators separated by 11 helical turns of DNA. Synergistic binding of repressor to separate sites on DNA results in looping, with the intervening DNA as a topologically closed domain containing the two promoters. A closed DNA loop of 11 helical turns, which is in-flexible to torsional changes, disables the promoters either by resisting DNA unwinding needed for open complex formation or by impeding the processive DNA contacts by an RNA polymerase in flux during transcription initiation. Interaction between two proteins bound to different sites on DNA modulating the activity of the intervening segment toward other proteins by allostery may be a common mechanism of regulation in DNA-multiprotein complexes.Communication between proteins bound to spatially separated sites on DNA appears to be a ubiquitous mechanism governing regulation of cellular macromolecular processes, such as transcription, recombination, and DNA replication in both prokaryotes and eukaryotes (1-7). It involves a direct contact between homologous or heterologous proteins, giving rise to cooperative binding. In such mechanisms, DNA usually facilitates interaction between the DNA-bound proteins, providing a tether to increase the effective local concentration of the proteins. The DNA part of the looped complex has been viewed traditionally as a passive participant of regulation, merely aiding the formation of the correct DNA-multiprotein complexes.The gal operon of Escherichia coli contains two promoters, P1 and P2, separated by only 5 bp, and two operators, OE and O0, which are centered at -60.5 and +53.5 bp, respectively, from the transcription start site of P1 (refs. 8,and 9; Fig. 1). Gal repressor (GalR) negatively regulates transcription from P1 and P2 by repressing transcription from each promoter. For complete repression, GalR must bind to both OE and O,. A chimeric gal operon carrying a lac operator, which interacts with Lac repressor (Lacd), in the place of either one of the gal operators cannot be repressed when provided with both Gal and Lac repressors (10). However, when bothgal operators are replaced by lac operators, the operon can be repressed by LacI, suggesting that an interaction between the DNA-bound proteins may be essential in establishing repression and such interaction only happens between homologous repressors. In vitro transcription studies have shown that a complete repression of both gal promoters can be obtained only if the two operator-bound repressors associate, thereby forming a loop of the intervening DNA (11). Such association occurs with wild-type Lacd, which is a tetramer and capable of binding to two operators simultaneously (11-16). Since wild-type GalR is a dimer, it requires another factor for DNA looping and the associated repression of both promoters (refs. 11 and 17; unpublished data). Wild-type GalR without the looping factor and a mutant Lacd (Lacladi), which is defective in tetramerization but binds t...

<0.1 g/t, 은품위가 평균 5.7 g/t으로 은적광산(금; 12.3 g/t, 은; 1,380.0 g/t) 과 상은광산(금; 2.7 g/t, 은; 23.5 g/t)에 비해 남측으로 가면서 금, 은의 품위는 현저히 떨어지는 반면, 그 외 연, 아연 등 유화광물 함량은 증가하는 양상을 보인다.핵심어: 영암광화대, 은적-상은 광상, 석영맥, 북북서-남남동 방향, 금-은 광화작용 Abstract: The Yeongam mineralized zone is located in the southwestern part of the Korean peninsula, including the Sangeun, Eunjeok and Baramjai mines. This zone is located in the northeastern part of the Mokpo-Haenam-Yeongam volcanic circular structure. The 13 sites of quartz vein with mineralization are developed in the Sangeun-Eunjeok-Baramjai area, within rhyolitic welded tuff, showing N-S or NNW trend with highly dipping to the west. The quartz veins occur as a single vein or a bundle of veins with width of 1-5 cm in each. The existence of faults parallel to the quartz veins indicates that the faulting occurred before and after the development of quartz veins and mineralization. The quartz veins and mineralized zone are displaced by NW-trending sinistral strike-slip faults. The extension of the SangeunEunjeok mineralized belt is traced to the south, following a NNW-trending tectonic line, and the Au-Ag contents are analysed in the 12 sites of quartz veins. Contents of gold and silver are 12.3 g/t and 1,380.0 g/t in Eunjeok mine, 2.7 g/t, 23.5g in Sangeun mine, and <0.1 g/t, 5.7 g/t in Baramjai mine respectively. Therefore, a highly Ag-Au mineralized zone is not developed in the southern part of the studied area.