Response to Hammer et al.: Tuning genetic control – importance of thorough promoter characterization versus generating promoter diversity

The expression level of a particular gene can span a continuum of expression levels, but gene function is typically studied at only a few discrete points in this continuum, such as strong overexpression or knockout. [...]the statement by Hammer et al. that our mutagenesis technique results in less than 0.1% functional clones does not accurately represent our results.