elements and protein-coding sequences can operate over large distances (even between different chromosomes) [149]–[152], suggesting the involvement of a trans-acting signal. Moreover, many promoter elements that exhibit transvection are transcribed into ncRNAs, and transvection is altered in Polycomb and zeste mutants [125]–[127],[130], indicating that epigenetic processes (which may be regulated by ncRNAs, see below) are involved. Taken together, these observations raise the possibility that transvection is mediated by trans-acting RNAs [153], in which case the observed cross-complementation may occur simply as a result of a compound heterozygosity between a regulatory ncRNA locus and a nearby protein-coding locus whose expression is controlled by it.
