engleski

Evolution of centromere

The centromere is a region of the chromosome that enables the accurate partition of newly replicated sister chromatids between daughter cells during mitosis and meiosis. It holds sister chromatids together and through its centromere DNA-protein complex known as the kinetochore, binds spindle microtubules to bring about accurate chromosome movements. Comparison of centromeric DNA sequences and proteins reveals a homology of proteins among evolutionary distant organisms while centromeric DNA sequences differ significantly and evolve rapidly during speciation. Such a plasticity of centromeric DNA could be explained by epigenetic control of centromere function which does not depend absolutely on primary DNA sequence but might be caused by modifications of chromatin. Although existing data favour centromere being epigenetic structure it is also clear that centromere formation is based on DNA, in particular tandemly repeated satellite DNA and its transcripts. Presence of conserved structural motifs within centromeric DNAs such as periodically distributed AT tracts, protein binding sites or promoter elements indicate that despite sequence flexibility, there are structural determinants which are prerequisite for centromere function. In addition, existence of functional centromeric DNA transcripts indicates possible importance of structural elements at the level of RNA secondary or tertiary structure. Rapid centromere evolution is explained by a stochastic process induced by homologous recombination followed by extrachromosomal rolling circle replication. As a result of such process amplification of different repetitive sequences already present within a genome occurs. However, only those sequences which have inherent centromere-competence in the form of structural requirements necessary for centromere function are after amplification fixed in a population as a new centromere.

centromere; evolution

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