Scientists have made a start toward creating a parallel biological universe by synthesizing a d-DNA polymerase, the enantiomer of natural l-DNA polymerase. When supplied with enantiomeric DNA building blocks (l-deoxyribonucleoside triphosphates) and a corresponding l-DNA primer and l-DNA sequence, the synthetic polymerase creates a faithful copy of the nonnatural l-DNA strand. The d-polymerase also recognizes nonnatural RNA building blocks, so it also transcribes the l-DNA sequence into an l-RNA strand in the presence of l-ribonucleoside triphosphate building blocks. Taking a further step toward mirror-image life by translating l-RNAs into nonnatural d-proteins would require a mirror-image ribosome—which would take considerably more effort to create, says Ting F. Zhu of Tsinghua University, who carried out the study with colleague Lei Liu and coworkers (Nat. Chem. 2016, DOI: 10.1038/nchem.2517). Potential applications of such mirror-image life would include bacteria that could biosynthesize difficult-to-make chiral drugs and biomolecules. A highlight of the study was the team’s demonstration that when natural and nonnatural DNA polymerases are put in the same pot with starting materials and strands of both chiral types, they operate simultaneously and totally independently to copy their own forms of DNA, showing that parallel biological universes can coexist.