Free genes for rRNAs in the macronuclear genome of the ciliate Stylonychia mytilus.

When separated on an agarose gel, macronuclear DNA of the hypotrichous ciliate Stylonychia mytilus gives rise to many well-defined bands ranging in molecular weight from 0.3 x 10(6) to 14 x 10(6) dalton. Hybridization of 25 S rRNA, 17S rRNA or 5 S RNA to such a gel revealed sharp hybridization bands. This suggests that this banding pattern is not an artefact due to nonspecific degradation of macronuclear DNA but that the DNA in the macronucleus of Stylonychia occurs in discrete fragments, each coding for at least one gene. The size of the DNA fragment coding for rRNA was found to be 4.5 x 10(6) dalton, the fragment coding for 5 S RNA has a molecular weight of 150,000-250,000 dalton.