The mosquito larvicidal binary toxin produced by Bacillus sphaericus is composed of 2 proteins called BinA and BinB. While BinB acts as specificity determinant, BinA is expected to bind to BinB, translocates into cytosol, and exerts its activity via an unknown mechanism. To study the role of cysteine in BinA, 3 cysteine residues were substituted by alanine and serine. Substitution at Cys195 significantly reduced the toxin activity, whereas substitution at Cys31 and Cys47 abolished its toxicity. Intrinsic fluorescent analysis suggested that all mutant proteins should have similar tertiary structure to that of the wild type. Analysis of the mutant protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with and without a reducing agent indicated that all 3 cysteine residues were not involved in disulfide bond formation within the BinA molecule. This is the first report to demonstrate that cysteine residues at 3 positions in BinA are required for full toxicity of the binary toxin. They may play a critical role during oligomerization or interaction between BinA and BinB to form the active complex.

Epigenetic and chromatin modifications have important roles in governing gene activity and nuclear architecture. They are also necessary for normal embryonic development and cell differentiation. Early epigenetic programming events during mouse embryogenesis are believed to be essential for normal growth and development. Aberrant epigenetic profiles are associated 2 with the conversion of normal cell phenotypes into cancer cells. Because epigenetic alterations are potentially reversible, experimental progress in this area may offer great promise for new cancer therapy. Nuclear epigenetic profiles can be manipulated using techniques such as somatic cell reprogramming, genetic engineering and small molecules, which can reprogramme the cell towards dedifferentiation and transdifferentiation. Advances into the mechanisms will improve the potential for regenerative medicine. In this review, we describe the principles of epigenetics and its relation to cell reprogramming, differentiation, dedifferentiation and transdifferentiation.