High frequency repeat-induced point mutation (RIP) is not associated with efficient recombination in Neurospora

Area of Science:

• Genetics
• Molecular Biology
• Mycology

Background:

• Repeat-induced point mutation (RIP) is a DNA repair process in Neurospora crassa that targets duplicated sequences during the sexual cycle.
• Previous studies suggested a link between RIP and homologous recombination, particularly for linked, direct DNA duplications.

Purpose of the Study:

• To investigate the relationship between RIP and homologous recombination using unlinked, inverted, and direct linked duplications in Neurospora crassa.
• To determine if RIP can inactivate adjacent single-copy genes.

Main Methods:

• Analysis of RIP and recombination frequencies in progeny from crosses involving different types of DNA duplications.
• Sequence analysis and Southern blotting to examine mutation spread and location.

Main Results:

• RIP occurred at high frequencies (42-100%) for all tested duplications.
• Homologous recombination was infrequent, occurring at frequencies one to three orders of magnitude lower than RIP.
• A single-copy gene located between linked duplications was inactivated by RIP at moderate frequencies (12-14%), with mutations spreading significantly beyond the duplication boundary.

Conclusions:

• RIP and homologous recombination are distinct processes in Neurospora crassa, with RIP being far more frequent.
• RIP can inactivate genes located in single-copy sequences adjacent to duplications, with mutations spreading considerable distances.
• The correlation between RIP and recombination in direct duplications suggests a potential mechanistic association or sequential activation.