Marburg virus entry consists of three distinct phases: cellular attachment, endocytosis, and fusion ( Figure 7) . Based on the sequence similarity between EBOV and MARV GPs many investigators have presumed identical functions and characteristics between the filovirus glycoproteins. This is presumptuous given the differences in glycosylation and sialic acid linkages [85] and dependence upon endosomal proteases (see below, 8.1.2. Endocytosis). Despite the existence of a number of detailed studies and structural analyses of EBOV GP [162] [163] [164] [165] , relatively few mechanistic studies of MARV GP have been performed [101] , although one recent post-fusion structure of MARV GP 2 has been reported [97] . The structure of MARV GP 2 is nearly identical to that of EBOV GP 2 , indicating that the mechanisms of fusion between the two viruses is likely conserved [97] . (2), GP 1 is cleaved by endosomal proteases (3) facilitating binding to NPC1, the entry receptor (4). Fusion is mediated in a pH-dependent manner by GP 2 . Following release of viral nucleocapsid into the cytosol (5), transcription of the viral genome takes place (6) . mRNA is subsequently translated by the host cell machinery (7) . Synthesis of GP takes place at the ER and undergoes multiple posttranslational modifications on its way through the classical secretory pathway (8) . Positive sense antigenomes are synthesized from the incoming viral genomes (9) . These intermediate products then serve as templates to replicate new negative sense genomes (10) . After cleavage in the Golgi, GP is transported to multivesicular bodies (MVB) and to the cell membrane where budding takes place (11) . Nucleocapsids and VP24 are also recruited to sites of viral budding (12) , which is driven by VP40 (13).