In vertebrate retinal photoreceptors, the rod outer-segment disc membranes contain densely packed rhodopsin molecules for optimal light absorption and subsequent amplification by the visual signalling cascade¹, but how these photon receptors are organized with respect to each other is not known. Here we use infrared-laser atomic-force microscopy to reveal the native arrangement of rhodopsin, which forms paracrystalline arrays of dimers in mouse disc membranes. The visualization of these closely packed rhodopsin dimers in native membranes gives experimental support to earlier inferences about their supramolecular structure^{2, 3} and provides insight into how light signalling is controlled.

1. M. E. Müller Institute for Microscopy, Biozentrum, University of Basel, Basel 4056, Switzerland
2. Department of Ophthalmology, University of Washington, Seattle, Washington 98195, USA
3. Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
4. Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
5. International Institute of Molecular and Cell Biology, and Department of Chemistry, University of Warsaw, Warsaw 02-109, Poland

Correspondence to: Krzysztof Palczewski^2,4,5 e-mail: Email: palczews@u.washington.edu