The binding of MC1 protein, the major chromosomal protein of the archaebacterium Methanosarcina sp. CHTI 55, to the region preceding the strongly expressed genes encoding methyl coenzyme reductase in a closely related micro-organism has been investigated. By gel retardation and DNAase I footprinting assays, we identified a preferential binding sequence in an open reading frame of unknown function. The large area of DNA protected against DNAase I is interrupted by a strong cleavage enhancement site on each strand. By circular permutation assays, we showed that the DNA bends upon MC1 binding. Furthermore we observed that the presence of a sequence outside the binding site can induce an unusual electrophoretic behaviour in some complexes.

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