DISTINGUISHING DNA AND PROTEIN IN BACTERIOPHAGE BY CRYO-SCANNING TRANSMISSION ELECTRON TOMOGRAPHY

Cryo-scanning transmission electron tomography (CSTET) is an emerging modality for 3D imaging in life sciences. Based on scanning transmission EM (STEM), a particular strength of the approach is its quantitative nature. Image contrast is based on electron scattering, which is a sensitive function of the atomic number Z as well as the density of material. Using an array of detectors that subtend different scattering angles, sensitivity can be optimized for relatively light or heavy elements. Elements such as phosphorus, calcium, iron, and zinc are easy to distinguish from the light elements that dominate organic matter: hydrogen, carbon, nitrogen, and oxygen. We aim to resolve subtle contrast differences between nucleic acids and protein on the basis of their distinct composition. We use T4 bacteriophage as a well-studied case where nucleic acid and protein are conveniently separated in space. In spite of the long study, very basic questions remain regarding the distribution of DNA within the capsid. We expect to shed new light on these issues using the new quantitative tomography.