Translesion DNA polymerases Pol ζ, Pol η, Pol ι, Pol κ and Rev1 are not essential for repeat-induced point mutation inNeurospora crassa

Abstract

Pol zeta, Pol eta, Pol iota, Pol kappa and Rev1 are specialized DNA polymerases that are able to synthesize DNA across a damaged template. DNA synthesis by such translesion polymerases can be mutagenic due to the miscoding nature of most damaged nucleotides. In fact, many mutational and hypermutational processes in systems ranging from yeast to mammals have been traced to the activity of such polymerases. We show however, that the translesion polymerases are dispensable for repeat-induced point mutation (RIP) in Neurospora crassa. Additionally, we demonstrate that the upr-1 gene, which encodes the catalytic subunit of Pol zeta, is a highly polymorphic locus in Neurospora.

Dominant Suppression of Repeat-Induced Point Mutation in Neurospora crassa by a Variant Catalytic Subunit of DNA Polymerase-ζ

“…Homozygous mus-26 mutant crosses are not ordinarily RIP defective (Tamuli et al 2006). We found that RIP was suppressed in the cross Srp; mus-26 (84) a 3 mus-26 (27); Dp(erg-3) A (frequency of erg-3 progeny ,0.5).…”

“…The largest candidate gene, NCU01951.1, also known as upr-1, had 118 nucleotide differences between its Adiopodoumé and OR alleles (upr-1 Ad and upr-1 ORA ), including 66 nonsynonymous changes. Crosses homozygous for RIP-induced mutants of upr-1 are RIP competent (Tamuli et al 2006), but this did not disqualify upr-1 Ad from being Srp.…”

“…Although Pol-z and the other translesion polymerases (Pol-h, Pol-i, Pol-k, and Rev1) are dispensable for RIP (Tamuli et al 2006), a RIP-suppressive Pol-z catalytic subunit encoded by upr-1 Ad might be well placed to interfere with the assembly of other factors essential for RIP in Neurospora. RIP suppression by upr-1 Ad did not require the Pol-z regulatory subunit encoded by mus-26.…”

“…They contain the hphtagged transgene Dp(dow) that duplicates a fragment of the LG IIIR gene downy (dow) and targets RIP to dow. The mus-26 (NcRev7) mutant strains were constructed in the laboratory and have been described by Tamuli et al (2006).…”

“…This finding revealed that at least a subset of upr-1 alleles can act as potential regulators of RIP. A role for upr-1 in RIP regulation could have driven its rapid evolution, as evidenced by the unusually high polymorphism exhibited by this gene in N. crassa (Tamuli et al 2006).…”