Fluorescence images were acquired with a Nikon Ti-U microscope using a 100X oil immersion apochromat TIRF objective (NA = 1.49) (Nikon Instruments, Melville, NY). A Spectra-X LED Light Engine (Lumencor, Beaverton, OR) was used for illumination, and an Andor iXon 897 EMCCD camera (Andor Technologies, Belfast, UK) with 16-bit image settings. Images were captured with Metamorph software version 7.10.4 (Molecular Devices, Sunnyvale, CA).