Dominant suppression of repeat-induced point mutation (RIP) in Neurospora crassa by a variant catalytic subunit of DNA polymerase zeta (Pol )

Crosses involving the Adiopodoumé strain of Neurospora crassa are defective for repeat-induced point mutation (RIP), a genome defense mechanism of fungi. We show here that the Adiopodoumé strain possesses an incompletely penetrant and variably expressive dominant suppressor of RIP (Srp) that maps to a ~34 kbp genome segment that is ~ 26 kbp proximal to mat on linkage group IL. Gene disruption experiments revealed that Srp is the upr-1 allele of Adiopodoumé (upr-1Ad) that is contained within this segment. The upr-1 gene codes for the catalytic subunit of the translesion DNA Polymerase zeta (Pol z) and it is unusually polymorphic in Neurospora. That the upr-1 gene contains upstream ORFs that overlap with the main ORF is potentially relevant to the incomplete penetrance and variable expressivity of the suppressor. Crosses between heterokaryons that contain upr-1Ad and strains that prevent mating events involving nuclei that contain upr-1Ad yielded no progeny in which RIP had occurred, consistent with the idea that the suppressor encoded by upr-1Ad is diffusible. The potential involvement of the Pol z subunit in two functions; translesion DNA synthesis and RIP regulation, might account for the rapid evolution of its gene in Neurospora.

Key Words: dominant suppression of RIP, metastable epiallele

Online ISS 1091-6490
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