10         20         30         40         50         60
         |          |          |          |          |          |
MEKFAPEFHG EDANNRATKF LESIKGKFTS PKDPKKKDSI ISVNSIDIEV TKESPITSNS - 60
TIINPTNETD DTVGNKPNYQ RKPLVSFKED PTPSDNPFSK LYKETIETFD NNEEESSYSY - 120
EEINDQTNDN ITARLDRIDE KLSEILGMLH TLVVASAGPT SARDGIRDAM VGLREEMIEK - 180
IRTEALMTND RLEAMARLRN EESEKMAKDT SDEVSLNPTS EKLNNLLEGN DSDNDLSLED - 240
F

Human respiratory syncytial virus (HRSV) possesses a single-stranded RNA genome of negative polarity of 15 222 nt. The pneumovirus genome, including that of HRSV, encodes some unique gene products, such as the nonstructural NS1 and NS2 proteins implicated in counteracting the interferon response, the 22 kDa (22K or M2-1) protein, which acts as a transcription anti-terminator factor, and the M2-2 protein implicated in modulating the switch between transcription and replication. It is thought that the template for RNA synthesis is the ribonucleoprotein (RNP) complex made of viral RNA (the genome) and the nucleoprotein (N), and that the large RNA-dependent RNA polymerase, encoded by the L gene, requires the phosphoprotein (P) as an essential cofactor. These three proteins, L, N and P, are required for genome replication but, in addition, the HRSV 22K protein is needed for efficient transcription. HRSV P is composed of 241 aa, much shorter than its counterparts from other paramyxoviruses. It is phosphorylated mainly at Ser-232. The precise role of phosphorylation for P activity remains unclear. HRSV P interacts with N and the RNA polymerase, and possibly with the 22K protein, playing a central role in the process of RNA synthesis. P interacts with newly synthesized N (N0) to prevent illegitimate assembly of the latter and to deliver it to the nascent chain during genome replication. In addition, it has been proposed that Sendai and measles virus P cartwheel on the RNP template via simultaneous breaking and reforming of contacts with N, opening the RNP structure so that the polymerase, tethered by P, can reach the bases in the viral RNA. The oligomeric nature of P is central to its interaction with the RNP template via simultaneous binding of multiple arms of the P oligomer with the exposed C-terminal tails of the assembled N monomers. Acts as a cofactor that serves both to stabilize the protein L and to place the polymerase complex on the N:RNA template.