The chromosomal protein MC1 from the archaebacterium Methanosarcina sp. CHTI 55 induces DNA bending and supercoiling.

We have investigated the effect on the DNA structure of protein MC1, a basic and small polypeptide (Mr 10700) representing the major chromosomal protein in Methanosarcinaceae. The ability of protein MC1 to strongly favour cyclization upon polymerization of short DNA fragments by T4 DNA ligase indicates that protein MC1 mediates DNA bending. Several negatively supercoiled topoisomers of minicircles were obtained with DNA fragments of 203 and 146 bp, their distribution depends upon the amount of protein MC1 complexed with DNA. In addition, protein MC1 can induce a compaction of a nicked plasmid

Archaebacterial histone-like protein MC1 can exhibit a sequence-specific binding to DNA.

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

Oxidation-sensitive residues mediate the DNA-bending activity of MC1 protein

The Methanosarcina thermophila MC1 protein is a small basic protein that is able to bend DNA sharply. When this protein is submitted to oxidative stress through gamma irradiation, it loses its original DNA interaction properties. The protein can still bind DNA but its ability to bend DNA is decreased dramatically. Here, we used different approaches to determine the oxidations that are responsible for this inactivation. Through a combination of proteolysis and mass spectrometry we have identified the three residues that are oxidized preferentially. We show by site directed mutagenesis that two of these residues, Trp74 and Met75, are involved in the DNA binding. Their substitution by alanine leads to a strong reduction in the protein capacity to bend DNA, and a total loss of its ability to recognize bent DNA. Taken together, these results show that oxidation of both these residues is responsible for the protein inactivation. Furthermore, the results confirm the strong relationship between DNA bending and recognition of DNA sequences by the MC1 protein

Propriétés de fixation de la protéine MC1 sur des minicercles d'ADN

National audienc