Abstract
The binding of lactose repressor to poly d(A-T) at low ionic strength has been investigated by heat denaturation. The poly d(A-T) melting is monitored by optical density and the protein melting by circular dichroism. From the modification of the poly d(A-T) melting curve we estimate a maximum binding ratio of about one tetrameric repressor to about 20 bases pairs. The repressor melting can be interpreted as a global shift from α to β structure of about 25 residues per subunit. The melting curves of poly d(A-T) and repressor have not a shape easy to interpret; nevertheless both show a cooperative transition in the same temperature range where we can evaluate that about 3.8 aminoacid residues shift from α to β structure when 1 basespair melt.
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Selected References
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