Human Ribosomal RNA Gene Arrays Are Switched On from One End: A Single-Molecule Census of the 45S and 5S rDNA Arrays

Humans make ribosomal RNA from two families of tandemly repeated genes: the 45S genes, in arrays on the short arms of five acrocentric chromosomes, and the 5S genes, in one array on chromosome 1q42. Only part of each family is active, but where the active copies sit inside an array could not be measured until complete genome assemblies and long reads made single copies addressable. We read public nanopore data from 479 genomes, using only molecules that start in unique DNA beside an array, so that every gene can be numbered from that end, and called each gene on or off from CpG methylation.