The M2-2 protein of human respiratory syncytial virus is a regulatory factor involved in the balance between RNA replication and transcription.
The M2 mRNA of human respiratory syncytial virus (RSV) contains two overlapping ORFs, encoding the transcription antitermination protein (M2-1) and the 90-aa M2-2 protein of unknown function. Viable recombinant RSV was recovered in which expression of M2-2 was ablated, identifying it as an accessory factor dispensable for growth in vitro. Virus lacking M2-2 grew less efficiently than did the wild-type parent in vitro, with titers that were reduced 1, 000-fold during the initial 2-5 days and 10-fold by days 7-8. Compared with wild-type virus, the intracellular accumulation of RNA by M2-2 knockout virus was reduced 3- to 4-fold or more for genomic RNA and increased 2- to 4-fold or more for mRNA. Synthesis of the F and G glycoproteins, the major RSV neutralization and protective antigens, was increased in proportion with that of mRNA. In cells infected with wild-type RSV, mRNA accumulation increased dramatically up to approximately 12-15 hr after infection and then leveled off, whereas accumulation continued to increase in cells infected with the M2-2 knockout viruses. These findings suggest that M2-2 mediates a regulatory "switch" from transcription to RNA replication, one that provides an initial high level of mRNA synthesis followed by a shift in the RNA synthetic program in favor of genomic RNA for virion assembly. With regard to vaccine development, the M2-2 knockout has a highly desirable phenotype in which virus growth is attenuated while gene expression is concomitantly increased.
Bermingham
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A
Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, 7 Center Drive MSC 0720, Bethesda, MD 20892-0720, USA.
Collins
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PL
D000595:Amino Acid Sequence; D000956:Antigens, Viral / Q000032:analysis; D015152:Blotting, Northern; D015707:HN Protein; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D012333:RNA, Messenger / Q000032:analysis; D012367:RNA, Viral / Q000032:analysis / Q000096:biosynthesis*; D018113:Respiratory Syncytial Virus, Human / Q000235:genetics* / Q000276:immunology; D014158:Transcription, Genetic; D014759:Viral Envelope Proteins; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
D000956:Antigens, Viral; D015707:HN Protein; D012333:RNA, Messenger; D012367:RNA, Viral; D014759:Viral Envelope Proteins; D014764:Viral Proteins; C116204:attachment protein G