  The ability to precisely edit genomes by deleting or adding genetic
information enables the study of biological functions and the building of
efficient cell factories. In many unconventional yeasts, such as promising new
hosts for cell factory design but also human pathogenic yeasts and food
spoilers, this progress has been limited by the fact that most yeasts favor
non-homologous end joining (NHEJ) over homologous recombination (HR) as DNA
repair mechanism, impairing genetic access to these hosts. In mammalian cells,
small molecules that either inhibit proteins involved in NHEJ, enhance protein
function in HR, or molecules that arrest the cell cycle in HR-dominant phases
are regarded as promising agents for the simple and transient increase of
HR-mediated genome editing without the need for a priori host engineering. Only
a few of these chemicals have been applied to the engineering of yeast although
the targeted proteins are mostly conserved; making chemical agents a yet
underexplored area in enhancing yeast engineering. Here, we consolidate
knowledge of available small molecules that have been used to improve HR
efficiency in mammalian cells and the few ones that have been used in yeast. We
include available high throughput (HTP)-compatible NHEJ/HR quantification
assays that could be used to screen for and isolate yeast-specific inhibitors.
