An internal ribosome entry site located upstream of the crucifer-infecting tobamovirus coat protein (CP) gene can be used for CP synthesis in vivo

Abstract

It was previously shown that, unlike the type member of the genus Tobamovirus (TMV U1), a crucifer-infecting tobamovirus (crTMV) contains a 148 nt internal ribosome entry site (IRES)CP,148 CR upstream of the coat protein (CP) gene. Here, viral vectors with substitutions in the stem–loop (SL) region of CP subgenomic promoters (TMV U1-CP–GFP/SL-mut and crTMV-CP–GFP/SL-mut) were constructed and the levels of CP synthesis in agroinoculation experiments were compared. No CP–GFP (green fluorescent protein) synthesis was detected in Nicotiana benthamiana leaves inoculated with TMV U1-CP–GFP/SL-mut, whereas a small amount of CP–GFP synthesis was obtained in crTMV-CP–GFP/SL-mut-injected leaves. Northern blots proved that both promoters were inactive. It could be hypothesized that IRES-mediated early production of the CP by crTMV is needed for realization of its crucifer-infecting capacity.