Previously, it has been shown that tobacco mosaic virus (TMV) U1 and crucifer-infecting TMV contain a 75 nt internal ribosome entry site (IRES) upstream of movement protein (MP) gene (IRES(U1)(MP,75) and IRES(CR)(MP,75), respectively). A movement-deficient TMV mutant, KK6, has been constructed previously [Lehto, K., Grantham, G. L. & Dawson, W. O. (1990). Virology 174, 145-157] by insertion of the second coat protein subgenomic promoter (CP SGP-2) upstream of the MP gene, in addition to the natural CP SGP-1. Here, the authors compare the efficiency of movement function expression by KK6 and a derivative, K86, obtained by insertion of IRES(CR)(MP,75) between the CP SGP-2 and MP genes resulting in restoration of IRES(CR)(MP,75) function in the 5'-untranslated sequence of the I(2) subgenomic RNA of K86. The data indicate that the efficiency of K86 movement was largely restored by this insertion, which was apparently due to the translation-enhancing ability of IRES(CR)(MP,75).
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