Sendai Virus Gene Start Signals Are Not Equivalent in Reinitiation Capacity: Moderation at the Fusion Protein Gene

Abstract

In paramyxovirus transcription, viral RNA polymerase synthesizes each monocistronic mRNA by recognizing the gene start (S) and end (E) signals flanking each gene. These signal sequences are well conserved in the virus family; nevertheless, they do exhibit some variations even within a virus species. In Sendai virus (SeV) Z strain, the E signals are identical for all six genes but there are four (N, P/M/HN, F, and L) different S signals with one or two nucleotide variations. The significance of these variations for in vitro and in vivo replication has been unknown. We addressed this issue by SeV reverse genetics. The luciferase gene was placed between the N and P gene so that recombinant SeVs expressed luciferase under the control of each of the four different S signals. The S signal for the F gene was found to drive a lower level of transcription than that of the other three, which exhibited comparable reinitiation capacities. The polar attenuation of SeV transcription thus appeared to be not linear but biphasic. Then, a mutant SeV whose F gene S signal was replaced with that used for the P, M, and HN genes was created, and its replication capability was examined. The mutant produced a larger amount of F protein and downstream gene-encoded proteins and replicated faster than wild-type SeV in cultured cells and in embryonated eggs. Compared with the wild type, the mutant virus also replicated faster in mice and was more virulent, requiring a dose 20 times lower to kill 50% of mice. On the other hand, the unique F start sequence as well as the other start sequences are perfectly conserved in all SeV isolates sequenced to date, including highly virulent fresh isolates as well as egg-adapted strains, with a virulence several magnitudes lower than that of the fresh isolates. This moderation of transcription at the F gene may therefore be relevant to viral fitness in nature.

Coordinate Deletion of N-Glycans from the Heptad Repeats of the Fusion F Protein of Newcastle Disease Virus Yields a Hyperfusogenic Virus with Increased Replication, Virulence, and Immunogenicity

“…Previously, a hyperfusogenic phenotype was also observed with mutants of the F protein of parainfluenza virus 5 (previously called simian virus 5) in which the fusion peptide was modified by glycine-to-alanine substitutions, suggesting that the native glycine residues serve to reduce the efficiency of fusion (15). Wild-type Sendai virus also downregulates its fusion activity, in this case due to a difference in a transcription gene start signal that results in reduced F gene transcription and protein expression; correction of this difference results in a virus that replicates more efficiently and is more lethal (17). A number of other paramyxoviruses also downregulate F expression (5,40,42).…”

Long Untranslated Regions of the Measles Virus M and F Genes Control Virus Replication and Cytopathogenicity

“…Interestingly, it has been reported that Sendai virus (SeV) and human parainfluenza virus type 1 (hPIV1) also possess strategies to inhibit production of the F protein (8,24). Kato et al showed that SeV inhibits production of the F protein and its downstream H and L proteins by having a unique GS signal at the F gene and thus reducing the reinitiation rate of transcription at the M-F gene boundary (24). The mutant SeV, in which the GS signal at the F gene was replaced by the common GS signal found at the P, M, and HN genes, replicated more efficiently and showed higher virulence in mice than the parental SeV (24).…”

Engineering of Live Chimeric Vaccines against Human Metapneumovirus

“…As it has been documented in numerous studies, the GS and GE signals of the vector virus can efficiently direct the expression of an exogenous protein [60]. Although GS and GE signals are often highly conserved along the viral genome, there might be variations in their sequences and transcription efficacy [142]. Flanking the sequence of GFP inserted into the 6 th genome position of PIV5 with GS/GE specific for either 2 nd or 7 th gene junctions resulted in large differences The 5'-end of a genome contains a trailer sequence (tr) of a variable length, ranging from 50 up to 707 nucleotides [121,133].…”