The occurrence of a soluble protein (E1) in cucumber cotyledons infected with plant viruses

Analysis on polyacrylamide gels of the soluble protein fraction of cucumber cotyledons infected with tomato spotted wilt virus (TSWV) revealed a stimulated protein component, designated as protein E₁. The amount of protein E₁ was related to the size and number of local lesions produced on the inoculated cotyledons. Protein E₁ stained positive for carbohydrate and could be partly purified by gel filtration on Sephadex G 100. The molecular weight was estimated to be approximately 22000 d. Protein E₁ seems to be serologically unrelated to any of the structural proteins of TSWV. Following inoculation of cucumber cotyledons with the yellow strain of cucumber mosaic virus (CMV), a protein with identical mobility on 7.5 and 10% polycrylamide gels to protein E₁ was detected. These proteins are probably identical and their accumulation is a result of the infection process. There was a close correspondence between the amount of protein E₁ and the severity of symptom expression. A protein with a mobility differing slightly from protein E₁ occurred in the soluble protein fraction ofNicotiana rustica after infection with either TSWV or tobacco mosaic virus.