Skip to content
Login Register

#HO endonuclease

2 public questions tagged with this topic.

Recombination

HO endonuclease cleaves

Mating type switching requires precise double-strand break initiation at active MAT locus. HO endonuclease is highly specific endonuclease expressed transiently in mother cells during late G1. It recognizes long degenerate 24 base-pair site spanning Ya/Z1 region at MAT, cleaving to generate 4 nucleotide 3' overhangs. Following cleavage, resection proceeds and strand invades silent donor cassette. HML and HMR themselves resist HO cleavage because heterochromatin and Sir proteins protect and because cleavage site degraded after donor copying. Thus HO activity is restricted to MAT enabling controlled conversion.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 7: HO Endonuclease Cleavage at MAT Locus

View Details
Recombination

Mating type switching in yeast occurs at which locus?

Saccharomyces cerevisiae haploids maintain mating type via single active MAT locus on chromosome III encoding regulators for a or alpha phenotype. Switching involves regulated replacement of MAT sequences. HML and HMR loci contain silent copies of both mating types embedded in heterochromatin near telomeres and not expressed. HO endonuclease induced double-strand break at MAT triggers recombination using HML/HMR as donor template copying opposite mating information into MAT. Therefore actual site of switching event where expression changes occurs at MAT, while silent cassettes serve merely as information reservoirs.

Ref: Watson et al., Molecular Biology of the Gene, 7th ed., Chapter 18: Yeast Mating Type Switch at MAT Locus

View Details