This paper describes the use of microtubules (MTs) as nanoscale templates for the biologically directed growth and assembly of cadmium sulfide (CdS) nanotubes. CdS is a wide bandgap semiconductor with valuable optical, electronic, and chemical properties, and the organization of CdS nanostructures is critical to their widespread utility. The present work explores a bioinspired, biomediated approach to the formation and assembly of CdS nanotubes. In particular, a biomimetic synthetic strategy is used to control the uniform growth of cubic zinc blende CdS nanocrystals on MT templates, replicating the MTs' tubular morphology with dense CdS only a single nanocrystal thick. Furthermore, specific interactions between MTs and functional microtubule-associated proteins (MAPs) are exploited to manipulate the secondary organization of these MT templates. The subsequent directed growth of CdS nanotubes on these structures produces specific biomediated architectures including linear arrays, 3D asters, and rings. Finally, cathodoluminescence from MT-templated CdS structures verifies that the valuable semiconducting character of these materials is exhibited. These demonstrations of nanoscale materials synthesis and assembly illustrate a new level of complexity and control over materials synthesis that may be achieved using such biological tools and processes.