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, s imilar to 43 amino acids) of an attenuated zucchini yellow mosaic potyvirus (ZYMV-AGII) coat protein (CP) were used to elucidate its role in viral sys temic infection. Deletion mutants truncated by 8, 13, and 33 amino acid res idues from the CP-NT 5 ' end were systemically infectious and produced symp toms similar to those of the AGH virus. Tagging these deletion mutants with either human c-Myc (Myc) or hexahistidine peptides maintained viral infect ivity. Similarly, addition of these peptides to the intact AGII CP-NT did n ot 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-t agged CP-NT deletion mutants, including those from which virtually all the viral CP-NT had been eliminated,, were able to encapsidate and cause system ic infection. Furthermore, chimeric viruses with deletions of up to 33 amin o 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 n ot permit systemic infection. However, fusion of the Myc peptide to the N t erminus of the FMDV peptide restored the capability of the virus to spread systemically. We have demonstrated that all CP-NT fused peptides were expos ed on the virion surface, masking natural CP immunogenic determinants. Our findings demonstrate that CP-NT is not essential for ZYMV spread and that i t can be replaced by an appropriate foreign peptide while maintaining syste mic infectivity.