Are DNA spacers relics of gene amplification events?

The genome of a thermophilic fungus, Thermomyces lanuginosus, contains a tandemly arranged cluster of sequences that are approximately equal to 50% homologous with the cytoplasmic 5S RNA and that are selectable by hybridization techniques. Unlike typical pseudogenes, these sequences are not truncated; rather, they bear a limited sequence homology with the entire length of the 5S RNA and are oriented end to end without significant intervening sequences. We suggest that these are gene relics that were duplicated by a rolling circle-like mechanism and that have evolutionarily drifted to become gene spacers. Accordingly, we raise the possibility that this offers a fortuitous glimpse at the origins for many of the gene spacers in the eukaryotic genome.