Part of the human ribosomal RNA locus stabilizes a plasmid in yeast

Most yeast plasmids - particularly those containing chromosomal replicators (ARS) - are unstable and do not segregate equally to mother and daughter cells unless they contain centromeric sequences. We have screened a fraction of the human genome for sequences that stabilize YRp7, a plasmid containing ARS1. We selected a fraction which we hoped would be enriched in human centromeric sequences - the DNA attached to the nucleoskeleton. We obtained one human sequence that partially stabilized a yeast plasmid and, surprisingly, it contained sequences homologous to those coding for the 3′ end of 18s rRNA, the transcribed spacer and 5′ end of 28s rRNA. This sequence did not show any ARS activity nor did it increase the copy number of the plasmid and so probably improved partition of the plasmid between mother and daughter cells. It had no homology to yeast centromeres.