Polymeric nature of tandemly repeated genes enhances assembly of constitutive heterochromatin in fission yeast

A kinetic model evaluates the relationship between heterochromatin assembly, small RNA production, and histone methylation in fission yeast. Motivated by our recent experiments that demonstrate that the tandemly repeated genes become heterochromatin, here we show a theory of heterochromatin assembly by taking into account the connectivity of these genes along the chromatin in the kinetic equations of small RNA production and histone methylation, which are the key biochemical reactions involved in the heterochromatin assembly. Our theory predicts that the polymeric nature of the tandemly repeated genes ensures the steady production of small RNAs because of the stable binding of nascent RNAs produced from the genes to RDRC/Dicers at the surface of nuclear membrane. This theory also predicts that the compaction of the tandemly repeated genes suppresses the production of small RNAs, consistent with our recent experiments. This theory can be extended to the small RNA-dependent gene silencing in higher organisms.

Automated summary

In this study, a kinetic model was used to evaluate the relationship between heterochromatin assembly, small RNA production, and histone methylation in fission yeast. The theory of heterochromatin assembly was proposed by considering the connectivity of tandemly repeated genes along the chromatin in the kinetic equations of small RNA production and histone methylation. The theory predicts the steady production of small RNAs due to the polymeric nature of tandemly repeated genes and the compaction of these genes suppresses the production of small RNAs, which is consistent with recent experiments. This theory can be applied to small RNA-dependent gene silencing in higher organisms.