 Aca genes are preserved, and researchers are using them to identify Acr genes, but the function of the proteins they encode is not totally clear.The Acr-associated promoter produces high levels of Acr transcription just after the phage DNA injection into the bacteria takes place and, afterward, Aca proteins repress the transcription.If this wasn't repressed, the constant transcription of the gene would be lethal to the phage.