Enzymes, too, are proteins, and so are the transcription factors that regulate their production.

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And some proteins act as transcription factors, regulating the output of the genes themselves.

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That is because one of Dr Yamanaka's transcription factors, c-Myc, sometimes has the unfortunate side-effect of causing cancer.

ECONOMIST: Human embryonic stem cells

The activity of genes is controlled by proteins called transcription factors that are, themselves, the products of genes.

ECONOMIST: Human embryonic stem cells

At least, that was the case for mice, as he found by tinkering with various combinations of transcription factors until he discovered a set that would do the trick.

ECONOMIST: Human embryonic stem cells

The main thing to be said against the methods used by Dr Yamanaka and Dr Yu is the way that they persuade their experimental cells to churn out the appropriate transcription factors.

ECONOMIST: Human embryonic stem cells