Palindromic sequences in heteroduplex DNA inhibit mismatch repair in yeast

Abstract

Although single heterozygous markers in yeast usually segregate during meiosis in a 2:2 ratio, abberant 3:1 segregations occur quite frequently as a result of gene-conversion events. A second type of aberrant segregation, post-meiotic segregation, results from the segregation of two genotypes from a single haploid spore; in yeast such events are detected as sectored spore colonies and usually occur rarely. Post-meiotic segregation is thought to result from the replication of heteroduplex DNA formed during meiotic recombination. We report here that if the heteroduplex includes a palindromic insertion sequence, a high frequency of post-meiotic segregation results. This suggests that palindromic insertions are poorly repaired, which may be the result of hairpin-loop formation that affects the efficiency of repair of heteroduplex DNA.

Physical detection of heteroduplexes during meiotic recombination in the yeast Saccharomyces cerevisiae.

“…With few exceptions, heterozygous insertion or deletion mutations in yeast cells show very little PMS, suggesting that these single-stranded regions are usually efficiently recognized by cellular mismatch repair systems (9,20). We have previously shown that a mismatch resulting from a heteroduplex formed between a wild-type gene and a gene with a palindromic insertion leads to high frequencies of PMS (19). We interpret this result as indicating that the stem-loop or hairpin configuration expected for a heterozygous palindromic insertion in a heteroduplex is inefficiently recognized by cellular mismatch repair systems.…”

“…The plasmid pDN9 was constructed by cloning a XhoI-BglII fragment of the HIS4 gene in BamHI-SalI-treated YIp5 (19). The plasmid pDN11 was constructed by allowing the palindromic oligonucleotide DNO14 to self-anneal and then inserting the annealed product into the SalI site of pDN9; this Sall site is within the HIS4 coding sequence (Fig.…”

“…We also demonstrate that, although cruciform structures can be formed in vivo as a consequence of heteroduplex formation between DNA strands that contain different palindromic insertions, small palindromic sequences in homoduplex DNA are rarely extruded into the cruciform conformation. For our studies, we analyzed the HIS4 locus, which has an unusually high level of meiotic recombination in our genetic background (5,6,19,31). At two other recombination hotspots in yeast cells, ARG4 (28) and an ectopically located LEU2 locus (4), meiosis-specific double-strand breaks have been observed.…”

“…For our studies, we analyzed the HIS4 locus, which has an unusually high level of meiotic recombination in our genetic background (5,6,19,31). At two other recombination hotspots in yeast cells, ARG4 (28) and an ectopically located LEU2 locus (4), meiosis-specific double-strand breaks have been observed.…”

The histone methylase Set2p and the histone deacetylase Rpd3p repress meiotic recombination at the HIS4 meiotic recombination hotspot in Saccharomyces cerevisiae

“…The mutant his4-lop and his4-lopc are 26 bp palindromic insertions that result in inefficiently-repaired mismatches (61). Only those markers that are different from the haploid progenitor strains are shown.…”