 Components of the RNAi pathway are used in many eukaryotes in the maintenance of the organization and structure of their genomes . Modification of histones and associated induction of heterochromatin formation serves to downregulate genes pre @-@ transcriptionally ; this process is referred to as RNA @-@ induced transcriptional silencing ( RITS ) , and is carried out by a complex of proteins called the RITS complex . In fission yeast this complex contains argonaute , a <unk> protein <unk> , and a protein called <unk> of unknown function . As a consequence , the induction and spread of heterochromatic regions requires the argonaute and RdRP proteins . Indeed , deletion of these genes in the fission yeast S. pombe disrupts histone methylation and centromere formation , causing slow or stalled anaphase during cell division . In some cases , similar processes associated with histone modification have been observed to transcriptionally upregulate genes . 
