Tomato （Lycopslcon esculentum Mill.） plants grown in a greenhouse were irradiated with two different levels of UV-B, namely 8.82 （T1） and 12.6 kJ/m^2 per day （T2）. Ethylene production, 1-aminocyclopropane-1-carboxylate （ACC） content, 1-（malonylamino） cyclopvopane-1-carboxylic acid （MACC） content, gene expression of ACC aynthase （EC 4.4.1.14）, and ACC oxidase activity in tomato leaves were determined. The results Indicated that ACC content, the activity of ACC synthase and ACC oxidase, and ethylene production Increased continuously under low doses of UV-B radiation, whereas at high doses of radiation these parameters Increased during the first 12 d and then started to decrease. The MACC content increased continuously over 18 d under both doses of UV-B irradiation. The changes in ACC content, ACC synthaae activity, ACC oxidase activity, the transcriptional level of the ACC synthase gene, and ethylene production were consistent with each other, suggesting that ACC synthase was the key enzyme in ethylene biosynthesis and that ethylene production in tomato leaf tissues under UV-B radiation could be regulated by the expression of the ACC synthase gene. The results also indicate that the change in ethylene metabolism may be an adaptive mechanism to enhanced UV-B radiation.
Bovine infected-cell protein 0 (BICP0) encoded by bovine herpes virus 1 (BHV-1) immediate early gene is necessary for efficient productive infection, in a large part, because it activates all 3 classes of BHV-1 genes. It also has the ability to efficiently transactivate promoters that are not derived from BHV-1. To investigate the mechanism by which BICP0 achieves these effects, we expressed and purified BICP0 and its different mutants in E. coli. In vitro assays showed that both full-length BICP0 and its isolated RING finger domain induce the accumulation of polyubiquitin chains. Mutations within the RING finger region that abolish the in vitro ubiquitination activity also cause severe reduc- tions in BICP0 activity in other assays. Based on these, we conclude that BICP0 has the potential to act as an E3 ubiq- uitin ligase during viral infection and its RING finger do- main is necessary for this function. These strongly support the hypothesis that BICP0 might influence virus infection through its ability to interact with the ubiquitin-proteasome pathway.
