Evolution of KRAB-containing zinc finger proteins and their roles in species evolution.

The C2H2 zinc finger protein family, one of the largest families of transcription factor/transcriptional regulator in mammal, arose from a small ancestral group of eukaryotic zinc finger transcription factors through many repeated gene duplications accompanied by functional divergence. As the biggest subfamily of C2H2 zinc finger protein family, Kruppel-associated box-containing zinc finger proteins (KRAB-ZFPs) appeared at the period oftetrapod, expand rapidly along with species evolution, and take about 60% of the total C2H2 zinc finger proteins in human. During species evolution, the DNA binding ability of KRAB-ZFPs is changed while the KRAB-ZFPs-mediate transcriptional repression ability maintains stable under the evolution pressure. Moreover, multiple KRAB-ZFPs function synergistically with KAP1 on transcriptional silencing of retroelements, and the coevolution between KRAB-ZFPs and target retrotransposons restrict the jumping ability of the retroelements. In this review, we summarize the roles of KRAB-ZFPs duplication, the flexibility of zinc finger structure, transcriptional repression of KRAB-ZFPs/KAP1 and retroelement "jump" in promoting the divergence in regulatory network, stable genome change and species evolution, in order to reveal the characters and functions of KRAB-ZFPs in driving species evolution stably.

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