A nonviral peptide can replace the entire N terminus of zucchini yellow mosaic potyvirus coat protein and permits viral systemic infection

Systematic deletion and peptide tagging of the amino terminal domain (NT, similar to 43 amino acids) of an attenuated zucchini yellow mosaic potyvirus (ZYMV-AGII) coat protein (CP) were used to elucidate its role in viral systemic infection. Deletion mutants truncated by 8, 13, and 33 amino acid residues from the CP-NT 5 ' end were systemically infectious and produced symptoms similar to those of the AGH virus. Tagging these deletion mutants with either human c-Myc (Myc) or hexahistidine peptides maintained viral infectivity. Similarly, addition of these peptides to the intact AGII CP-NT did not affect viral life cycle. To determine which parts, if any, of the CP-NT are essential for viral systemic infection, a series of Myc-tagged mutants,vith 8 to 43 amino acids removed from the CP-NT were constructed. All Myc-tagged CP-NT deletion mutants, including those from which virtually all the viral CP-NT had been eliminated,, were able to encapsidate and cause systemic infection. Furthermore, chimeric viruses with deletions of up to 33 amino acids from CP-NT produced symptoms indistinguishable from those caused by the parental AGII virus. In contrast to CP NT Myc fusion, addition of the foot-and-mouth disease virus (FMDV) immunogenic epitope to AGII CP-NT did not permit systemic infection. However, fusion of the Myc peptide to the N terminus of the FMDV peptide restored the capability of the virus to spread systemically. We have demonstrated that all CP-NT fused peptides were exposed on the virion surface, masking natural CP immunogenic determinants. Our findings demonstrate that CP-NT is not essential for ZYMV spread and that it can be replaced by an appropriate foreign peptide while maintaining systemic infectivity.