Following his PhD, Klug moved to Birkbeck College in the University of London in late 1953, and started working with Rosalind Franklin in John Bernal's lab. This experience aroused a lifelong interest in the study of viruses, and during his time there he made discoveries in the structure of the tobacco mosaic virus. In 1962 he moved to the newly built Medical Research Council (MRC) Laboratory of Molecular Biology (LMB) in Cambridge. Over the following decade Klug used methods from X-ray diffraction, microscopy and structural modelling to develop crystallographic electron microscopy in which a sequence of two-dimensional images of crystals taken from different angles are combined to produce three-dimensional images of the target. In 1962 Klug was offered a teaching Fellowship at Peterhouse, Cambridge. He went on teaching after his Nobel Prize because he found the courses interesting and was later made an Honorary Fellow at the College.
Mathematical physicist and crystallographer distinguished for his contributions to molecular biology, especially the structure of viruses. Development of a theory of simultaneous temperature and phase changes in steels led him to apply related mathematical methods to the problem of diffusion and chemical reactions of gases in thin layers of haemoglobin solutions and in red blood cells. Then the late Rosalind Franklin introduced him to the x-ray study of tobacco mosaic virus to which he contributed by his application and further development of Cochran and Crick's theory of diffraction from helical chain molecules. Klug's most important work is concerned with the structure of spherical viruses. Together with D. Caspar he developed a general theory of spherical shells built up of a regular array of asymmetric particles. Klug and his collaborators verified the theory by x-ray and electron microscope studies, thereby revealing new and hitherto unsuspected features of virus structure.
In 2005 he was awarded South Africa's Order of Mapungubwe (gold) for exceptional achievements in medical science.