Respiratory syncytial virus RNA-directed RNA polymerase L (RSV L)

The Respiratory syncytial virus (RSV) RNA-directed RNA polymerase L is a large, multifunctional enzyme (~250 kDa) that serves as the catalytic core of the viral replication and transcription machinery (1, 11). It is responsible for synthesizing the viral RNA genome and transcribing subgenomic mRNAs, which are essential for the production of all viral proteins (5, 12). The L protein also possesses specialized domains for mRNA capping (polyribonucleotidyltransferase and methyltransferase) and polyadenylation, ensuring that viral transcripts are stable and translatable by the host cell (9, 12). Because it is a critical viral enzyme with no direct human homolog, it is a primary target for direct-acting antiviral drugs (2, 8). Therapeutic strategies include nucleoside analogs that cause chain termination and non-nucleoside inhibitors that bind to allosteric sites or enzymatic domains to halt viral propagation (4, 6). Effective inhibition of the L polymerase can significantly reduce viral load, potentially preventing severe complications like bronchiolitis and pneumonia in vulnerable populations such as infants and the elderly (2, 15).

Other names

L proteinLarge structural proteinReplicaseTranscriptaseRNA-dependent RNA polymeraseRdRp

Inhibition of viral RNA-dependent RNA polymerase activity, which blocks the synthesis of viral genomic RNA and mRNA transcripts. Some inhibitors specifically target the capping (polyribonucleotidyltransferase) or methyltransferase domains of the L protein to prevent the production of functional, stable viral mRNAs (5, 8, 9).