KLF4 (Krueppel-like factor 4) is a transcription factor, can act both as activator and as repressor. KLF4 binds the 5'-CACCC-3' core sequence of promoters, and also binds to its own promoter region of its own gene and can activate its own transcription. KLF4 regulates the expression of key transcription factors during embryonic development. KLF4 plays an important role in maintaining embryonic stem cells, in preventing their differentiation. POU5F1/OCT4, SOX2, MYC/c-Myc and KLF4 are the four Yamanaka factors. When combined, these factors are sufficient to reprogram differenciated cells to an embryonic-like state designated iPS (induced pluripotent stem) cells. iPS cells exhibit the morphology and growth properties of ES cells and express ES cell marker genes.