| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2004: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2003: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2002: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Plant villins, P-115-ABP and P-135-ABP, containing in a crude extract prepared from lily pollen. bound to a DNase I affinity column in the presence of Ca^<2+>, and were dissociated and eluted from the column with EGTA. Purified P-135-ABP accelerated the polymerization of G-actin in the presence of Ca^<2+>. These results indicated that P-135-ABP can form a complex with G-actin in the presence of Ca^<2+> and consequently acts as a nucleus or seed for polymerization of actin filaments. Furthermore, P-135-ABP caped an actin filament end, and severed or depolymerized filaments in the presence of Ca^<2+>. P-135-ABP has been shown to arrange actin filaments into bundles. Hence, like animal villin, P-135-ABP exerts various effects on actin in a Ca^<2+>-dependent manner. Based on an analysis of the primary structure of P-115-ABP, it is assumed that P-115-ABP also has similar activities to those of P-135-ABP. Hence, plant villin in pollen tubes is responsible for bundling actin filaments in shank region, where low concentrations of Ca^<2+> are present, while is involved in depolymerizing or severing actin filaments in apical regions, where relatively high concentrations of Ca^<2+> concentrations are present. In the presence of profilin, a low molecular weight G-actin binding protein, the acceleration of actin polymerization by P-135-ABP was not found. It is indicated that almost of G-actin form complex with profilin present at similar concentration to that of actin in the germinating pollen. Hence, it is reasonable to consider that actin-nucleation activity of plant villin is not exerted in pollen.
Villin is widely distributed in plant cells, such as tobacco cultured cells BY-2. Interestingly, villin is co-localized with not only actin-filament bundles, but also certain organelles considered to be plastides. Therefore, it is possible that plant villin is one of factor responsible in the positioning of the organelles in cells.
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