Intercellular mobility and homing of an archaeal rDNA intron confers a selective advantage over intron(-) cells of Sulfolobus acidocaldarius

Some intron-containing rRNA genes of archaea encode homing-type endonucleases, which facilitate intron insertion at homologous sites in intron(-) alleles. These archaeal rRNA genes, in contrast to their eukaryotic counterparts, are present in single copies per cell, which precludes intron homing within one cell. However, given the highly conserved nature of the sequences flanking the intron, homing may occur in intron(-) rRNA genes of other archaeal cells. To test whether this occurs, the intron-containing 23S rRNA gene of the archaeal hyperthermophile Desulfurococcus mobilis, carried on nonreplicating bacterial vectors, was electroporated into an intron(-) culture of Sulfolobus acidocaldarius. PCR experiments demonstrated that the intron underwent homing and spread through the culture. By using a double drug-resistant mutant of S. acidocaldarius, it was shown that spreading resulted partly from a selective advantage of intron(+) cells and partly from intercellular mobility of the intron and homing.