ed and cloned into the pIRES-puro Glue vector downstream of the tandem affinity tags. The p3FLAGCMV14 plasmid with human cDNA for TRAFD1 was a gift from Dr. Akihiko Yoshimura, Keio University, Tokyo, Japan). Deletion mutants of the cDNA were PCR-amplified and cloned into the p3FLAG-CMV14. A 6 cm dish of HEK293T cells was transfected with p3xFLAG-CMV14TRAFD1 and pIRES-puro GluePlekhm1, either full-length or deletion mutants using Lipofectamine 2000. 24 hours post-transfection, the cells were washed with ice-cold PBS twice and lysed in 0.5 ml of lysis buffer supplemented with fresh 2 mM DTT and protease inhibitor cocktail. Lysates were cleared by centrifugation and pull-downs were performed using 25 l of Streptavidin Sepharose for 2 hours at 4C. After extensive PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19666601 washing of beads with lysis buffer, precipitated proteins were detected by immunoblot analysis using chemiluminescent detection. For immunoprecipitation of FLAG-tagged TRAFD1, HEK293 cells were lysed with lysis buffer. 15 l of FLAG-M2 gel was incubated with cell lysate for 2 hours at 4 C and pellets were washed 5 times with wash buffer prior to loading onto SDS-PAGE gels for analysis. Immunofluorescence Cells grown on glass coverslips were fixed with 3% paraformaldehyde in PBS for 10 min, washed with PBS, permeabilized with 1% Triton X-100, and blocked with 1% BSA with 0.05% Tween 20 in PBS. Primary and secondary antibodies were diluted in blocking solution. Primary antibodies were used as follows: chicken anti-TRAFD1, rabbit anti-Plekhm1, goat anti-Rab7. All were incubated for 1 hour at room temperature and rinsed. Fluorescent dye-conjugated secondary antibodies were then incubated for 45 minutes. DAPI staining was used to label nuclei. The samples were mounted with ProLong Gold antifade reagent and observed with a Leica SP5 laser scanning confocal microscope equipped with 40 and 63 oil immersion lenses. Leica LAS AF Lite software was used for recording and image processing. RNA isolation and quantitative RT-PCR RNA was extracted using RNeasy and the yield determined by measuring OD260. 1 g of total RNA was subjected to reverse transcription with a QuantiTect Reverse Transcription Kit. The resulting cDNA was used for PCR using a QuantiFast SYBR Green PCR kit. Amplification Orange Yellow S chemical information Reactions were performed in triplicate in 10 l final volume that included the following: 1050 ng of template, 1 M primers, 2 SYBR Green Master Mix. Reactions were processed in a LightCycler 2: 95C for 5 min, then 40 cycles of 95C for 10 s and 60C for 30 s. Ct for each gene was calculated and represents the difference between the Ct value PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19667314 for the gene of interest and that of the reference gene. Fold-changes were calculated using the 
2-Ct convention. Primer sequences and the accession numbers of cDNA targets are shown in S1 Resorption assay Cells at a density 15,000/well were cultured for 10 days on Osteo Assay Surface 24-well plates under differentiation conditions. To observe 5 / 21 TRAFD1 in Osteoclast Activity resorption pits, plates were gently stripped of cells with 10% bleach, rinsed with distilled water, air dried, and scanned on a flatbed scanner. The percentage of resorbed area was analyzed by NIH ImageJ software. TRAP staining Fixed cells were TRAP-stained using a leukocyte acid phosphatase kit according to the manufacturer’s instructions. TRAP-positive multinucleated cells containing three or more nuclei were counted. TRAP activity assay RAW264.7 cells were cultured in -MEM containing RANKL on HA plate