 Identification of the transcription start site of a target gene and considering the preferences of sgRNA improves efficiency, as does the presence of accessible chromatin at the target site.Along with other improvements mentioned, factors such as the distance from the transcription start and the local chromatin state may be critical parameters in determining activation/repression efficiency.Optimization of dCas9 and sgRNA expression, stability, nuclear localization, and interaction will likely allow for further improvement of CRISPRi efficiency in mammalian cells.