YNT20, a bypass suppressor of yme1 yme2, encodes a putative 3'-5' exonuclease localized in mitochondria of Saccharomyces cerevisiae.

Mutation of YME genes in yeast results in a high rate of mitochondrial DNA escape to the nucleus. The synthetic respiratory growth defect of yme1 yme2 yeast strains is suppressed by recessive mutations in YNT20. Inactivation of YNT20 creates a cold-sensitive respiratory growth defect that is more pronounced in a yme1 background and which is suppressed by yme2. Inactivation of YNT20 causes a qualitative reduction in the rate of mitochondrial DNA escape in yme1, but not yme2, strains, suggesting that YNT20 plays a role in the yme1-mediated mitochondrial DNA escape pathway. YNT20p is a soluble mitochondrial protein that belongs to a subfamily of putative 3'-5' exonucleases. Furthermore, conserved sequence elements in Yme2p suggest that this protein may also function as an exonuclease.