Multifunctional protein that acts as a viral transcriptional activator. Promotes read-through of an RNA hairpin in the NP open reading frame to enhance viral transcription. Mechanistically, nonphosphorylated VP30 hexamers form a ternary complex with the viral leader RNA. Clamps the RNA template and the complex VP35-polymerase L together, thereby increasing the polymerase affinity for the RNA template to increase transcription initiation despite the presence of RNA secondary structures. Assists also stop-start transcription at gene junctions to promote transcription of downstream genes. Interaction with NP plays a critical role in transcription initiation by recognizing the RNA stem loop. Interaction with host RBBP6 interferes with NP-VP30 interaction and inhibits viral RNA synthesis. Also acts as a suppressor of RNA silencing by interacting with host DICER1 and TARBP2/TRBP