Figure 1.

Mode of action of diversity-generating retroelements (DGRs). DGRs always comprise an ORF encoding a reverse transcriptase (RT), a template repeat (TR) and at least one target ORF harboring the variable region (VR), which corresponds to the TR. First, an RNA transcript is made from the TR, which is then reversely transcribed by the RT in an error-prone fashion. In a process termed mutagenic homing, the mutagenized cDNA replaces the parental VR in the target ORF, thereby altering the host gene.