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,148CR upstream of the coat protein (CP) gene. Here, viral vectors with substitutions in the stemloop (SL) region of CP subgenomic promoters (TMV U1-CPGFP/SL-mut and crTMV-CPGFP/SL-mut) were constructed and the levels of CP synthesis in agroinoculation experiments were compared. No CPGFP (green fluorescent protein) synthesis was detected in Nicotiana benthamiana leaves inoculated with TMV U1-CPGFP/SL-mut, whereas a small amount of CPGFP synthesis was obtained in crTMV-CPGFP/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.