Analysis of tubulin metabolisms in fungi

l -2,5-二氢苯丙氨酸（DHPA）对曲霉的生长有抑制作用，并伴有形态改变。DHPA还诱导微管的消失和它们的单体α-和β-微管的细胞质池的丢失。DHPA可诱导所有微管蛋白基因的过表达。在dhpa处理的菌丝中，未检测到泛素化的小管蛋白，并且从菌丝中提取的无细胞提取物不会加速小管蛋白的降解。这些结果表明DHPA出乎意料地促进了微管蛋白基因的表达。我们还研究了DHPA对二态真菌白色念珠菌的影响。DHPA在菌丝诱导条件下抑制菌丝生长，然后诱导酵母细胞。一半的酵母细胞细胞核肿胀，细胞无明显的肌动蛋白斑块。另一方面，DHPA减少肌动蛋白、微管蛋白和泛素的池。这些结果表明DHPA对白色念珠菌的作用可能与对曲霉菌的作用不同。此外，我们还研究了减少微管蛋白库的药物对酿酒酵母的作用。异戊醇（IAA）也有这种效果。IAA诱导的假菌丝伴随a-和β-微管蛋白的相对缺失。虽然微管减少，但纺锤体微管没有明显消失，染色体分布似乎正常。然而，向子细胞分布的延迟发生了。此外，我们发现微管蛋白的减少不是由于微管蛋白基因转录的阻断和微管蛋白降解的加速，而是由于微管蛋白翻译的限制。结合上述结果，我们得出结论，药物诱导的微管蛋白丢失至少在三个真菌属中发现，并且这种丢失似乎与形态学改变有关。然而，我们没有在这些现象中找到共同的机制。

L-2,5-Dihydrophenylalanine (DHPA) shows the growth inhibition of Aspergillus spp. accompanying with morphological alterations. DHPA also induces the disappearance of microtubules and loss of the cytoplasmic pools of their monomeric α- and β-tubulins. DHPA was found to induce over-expression of all tubulin genes. In the DHPA-treated hyphae, ubiquitinated tubulins were not detected and cell free extracts from the hyphae did not accelerate the degradation of tubulins. These results suggest that DHPA unexpectedly facilitates the expression of tubulin genes.We also investigated the effect of DHPA on a dimorphic fungus Candida albicans. DHPA inhibited the hyphal growth under a hyphal inducible condition and then induced yeast cells. In addition, the half of the yeast cells had swollen nuclei and cells were also observed without apparent actin patch. On the other hand, DHPA reduecd the pools of actin, tubulin, and ubiquitin. These results indicate that the action of DHPA on C. albicans would be different from that on Aspergillus spp.Furthermore, we have searched drugs reducing tubulin pools against a budding yeast Saccharomyces cerevisiae. Isoamyl alcohol (IAA) was found to show such effects. IAA induced pseudohyphae accompanying with relative loss of a- and β-tubulins. Although decrease in tubulins was observed, spindle microtubule did not disappear apparently, and the distribution of chromosome seemed to proceed normally. However the delay of the distribution into daughter cells occurred. Moreover we found that decrease in tubulins was not due to the blockade of tubulin gene transcription and acceleration of tubulin degradation but the restriction of tubulin translation.Together with results obtained above, we concluded that drug-induced tubulin loss was found in at least three genuses of fungi and the loss seemed to be involved in morphological changes. However we did not find common mechanisms among such phenomena.