Influence of the Leader protein coding region of foot-and-mouth disease virus on virus replication

Abstract

The foot-and-mouth disease virus (FMDV) Leader (L) protein is produced in two forms, Lab and Lb, differing only at their amino-termini, due to the use of separate initiation codons, usually 84 nt apart. It has been shown previously, and confirmed here, that precise deletion of the Lab coding sequence is lethal for the virus, whereas loss of the Lb coding sequence results in a virus that is viable in BHK cells. In addition, it is now shown that deletion of the ‘spacer’ region between these two initiation codons can be tolerated. Growth of the virus precisely lacking just the Lb coding sequence resulted in a previously undetected accumulation of frameshift mutations within the ‘spacer’ region. These mutations block the inappropriate fusion of amino acid sequences to the amino-terminus of the capsid protein precursor. Modification, by site-directed mutagenesis, of the Lab initiation codon, in the context of the virus lacking the Lb coding region, was also tolerated by the virus within BHK cells. However, precise loss of the Lb coding sequence alone blocked FMDV replication in primary bovine thyroid cells. Thus, the requirement for the Leader protein coding sequences is highly dependent on the nature and extent of the residual Leader protein sequences and on the host cell system used. FMDVs precisely lacking Lb and with the Lab initiation codon modified may represent safer seed viruses for vaccine production.

Use of recombinant capsid proteins in the development of a vaccine against the foot-and-mouth disease virus

“…It is well known that interferon has a strong inhibitory effect on FMDV replication and studies have shown that expression of interferon, from adenovirus vectors, can effectively block FMDV replication in swine. 71 The precise deletion of the Lb coding region to make a socalled "leaderless virus" (see Figure 4) from FMDV results in a virus which is still viable [72][73][74] but attenuated in cattle. 75 The loss of Lb results in a decreased ability of the virus to shut off host cell protein synthesis; this will allow the synthesis of interferon.…”

“…75 The loss of Lb results in a decreased ability of the virus to shut off host cell protein synthesis; this will allow the synthesis of interferon. 76 Such viruses can grow well in BHK cells 73,74 and may represent useful tools for the development of safer vaccine strains for conventional cell culture production since any escape only releases viruses that are non-pathogenic and cannot revert to virulence. There has been significant interest recently in generating marked FMDVs which may permit improved DIVA and/ or offer alternative routes for virus purification.…”

Influence of Foot-and-Mouth Disease Virus O/CHN/Mya98/33-P Strain Leader Protein on Viral Replication and Host Innate Immunity

“…The length and secondary structure of La are conserved, while the nucleotides are highly variable (10). Furthermore, previous studies have demonstrated that La is involved in viral replication (7,30). L pro is a papain-like protease (20,32,38), and its two forms exhibit similar proteolytic activities (27,39).…”

Distance effects during polyprotein processing in the complementation between defective FMDV RNAs

“…However, mutation of the Lb AUG abolishes virus viability (Cao et al, 1995). The region between the two AUGs named 'spacer' region seems to be essential for some activity unrelated to its coding function, although deletion of the Lab 'spacer' region generates a functional Lb protease (Belsham, 2013).…”

“…This cleavage can also take place in trans. Construction of FMDVs with truncated L proteins showed that infectivity required that the residues that encode the N-terminus of VP4 be positioned directly following the second functional Lb AUG codon (Belsham, 2013;Piccone et al, 1995a), and the virus displayed reduced fitness. The deletion of the entire Lab-coding sequence with the Lab AUG positioned before the N-terminal Gly of VP4 resulted in a non-viable virus (Piccone et al, 1995a).…”