The role of MARV VP30 in viral transcription and replication is not well understood. In contrast to EBOV VP30, which plays an important role in regulating transcription initiation [68, 143, [155] [156] [157] , MARV VP30 is not essential for transcription or replication activity in a MARV minigenome system [113, 134] . Nevertheless, it seems to play an important role in viral amplification, since rescue of a full-length MARV clone is only successful in the presence of VP30 [158] . In addition, down-regulation of VP30 by RNA interference in MARV-infected cells led to the reduction of both viral protein synthesis and virion production [159] . Among the NNS RNA viruses, only the members of the subfamily Pneumovirinae possess a protein similar to VP30, M2-1, which functions as a transcription processivity factor [160] .