Tethering factors have emerged as key regulators of membrane traffic and organellar biogenesis. Herein, we explore the function of the p115 tethering factor operational at the ER-Golgi interface. We show that depletion of p115 disrupts the Golgi ribbon into fragments. The fragments form de novo adjacent to ER exit sites in cells subjected to BFA treatment and a subsequent wash-out, Significantly, the reformed Golgi fragments show cis- to trans- polarity. These results suggest that p115 is dispensable for traffic events generating differentiated Golgi fragments, but is required for fusion of such fragments into a Golgi ribbon. It appears that in vivo, the requirement for p115 is limited to later stages of ER-Golgi traffic. Previous studies documented that p115 coiled-coil 1 (CC1) region that binds a subset of ER-Golgi SNAREs and the Rab1 GTPase is required for Golgi biogenesis . Herein, we show that the CC1 domain is insufficient to sustain p115 function. We show that p115 mutants containing CC1 (and capable of binding SNAREs and Rab1), but lacking the CC4 coiled-coil domain act as dominant negatives and disrupt Golgi structure in cells containing endogenous p115. Furthermore, such mutants are unable to support Golgi biogenesis in cells depleted of endogenous p115. This suggests that CC4 is required for Golgi biogenesis. Significantly, CC4 has been shown to bind a subset of ER-Golgi SNAREs (Shorter et al., 2002). Our findings indicate that two non-overlapping SNARE-interacting domains within p115 are required for Golgi biogenesis. This supports a model in which p115 facilitates SNARE complex formation by using CC1 and CC4 to simultaneously bring two SNAREs into close proximity. We postulate that membrane tethering may occur through tether-mediated SNARE-SNARE linkage.