Molecular characterization of required for killing-2: a gene required for spore killing by Neurospora Sk-3.

The Sk-3 selfish genetic element in Neurospora fungi is transmitted to offspring in a biased manner through spore killing. In crosses between an Sk-3 strain and a Spore killing-sensitive (Sk-S) strain, nearly all offspring that fail to inherit Sk-3 are killed. Although a mutation called rfk-2UV, which disrupts spore killing by Sk-3, was isolated in an earlier work, its precise location within the Sk-3 element was not identified. Here, we demonstrate that rfk-2UV is a T>G transversion mutation within a protein coding gene called rfk-2. The rfk-2 gene is located on Chromosome III, and it encodes a transcript that undergoes RNA splicing and at least two RNA editing events. One of these editing events changes a UAG stop codon to a UGG tryptophan codon and allows for production of a 102 amino acid protein. Additionally, while our results demonstrate that rfk-2 is required for spore killing, they also show that it is insufficient for the process. Sk-3 is thus more complex than previously anticipated. Rather than using a single gene to produce its killer, Sk-3 requires multiple genes to kill spores and break the rules of Mendelian Inheritance.