Repeat-induced G-C to A-T Mutations in <i>Neurospora</i>

TLDR

In the Neurospora genome, duplicate sequences are detected and altered during the sexual phase. The study aims to characterize DNA alterations in duplicated sequences across sexual cycles. Duplicated sequences were isolated before and after one or more sexual cycles to assess these changes. RIP exclusively converts G‑C to A‑T mutations, preferentially at adenine 3′ to the changed cytosine, inactivating duplicate genes, altering restriction sites, and causing up to 50 % G‑C loss in linked duplications and ~10 % in distant ones.

Abstract

In the Neurospora genome duplicate sequences are detected and altered in the sexual phase. Both copies of duplicate genes are inactivated at high frequency, whether or not they are linked. Restriction sites change, and affected sequences typically become heavily methylated. To characterize the alterations of the DNA, duplicated sequences were isolated before and after one or more sexual cycles. DNA sequencing and heteroduplex analyses demonstrated that the process (termed RIP) produces exclusively G-C to A-T mutations. Changes occur principally at sites where adenine is 3′ of the changed cytosine. A sequence duplicated at a distant site in the genome lost approximately 10 percent of its G-C pairs in one passage through a cross. A closely linked duplication of the same sequence that was passed twice through a cross lost about half of its G-C pairs. The results suggest a mechanism for the RIP process.