Molecular Basis of Fruiting-body Formation in Basidiomycete Fungus

担子菌子实体的形成是微生物中观察到的最典型和最吸引人的形态分化之一。为了了解香菇(Shiitake)子实体形成的分子机制，我们研究了两个DNA结合转录因子Prib和Le.CDC5的靶基因，这两个转录因子都调节子实体的形成。Prib蛋白与16-bp的序列结合，共同序列为5‘GGGGGGACAGGGANCC3’，Le.CDC5蛋白与7-bp的序列结合，Consensus序列为5‘GCAATGT3’。MFBA也是一种调控子实体形成的有趣蛋白质，具有RGD序列、PHD指和SET结构域。因此，我们对MFBA蛋白的性质进行了研究。对于Prib、Le.CDC5和MFBA，我们得到了以下结果。(1)确定了Prib蛋白的三个靶基因：Prib、UMP-CMPK基因uck1和酿酒酵母YJRO070c的同源物mfbC。Mfbc基因是cons…。更多的是编码与推测的翻译起始因子eIF5A相互作用的蛋白质。只有成熟的子实体才有mfbC基因的转录本，这表明mfbC基因可能在子实体形成的最后阶段发挥作用。MfbC转录本在细胞器(鳃组织)中呈区域特异性分布。在TRAMA的外部区域检测到高水平的mfbC转录本，该区域是分支到膜下的区域。(2)分离到两个基因组HindIII片段，分别为3.7kb和3.9kb，与Le.CDC5蛋白结合。这两个片段含有几个7bp的一致序列，并与Le.CDC5蛋白结合。它们包含两到三个功能未知的基因。(3)MFBA蛋白的PhD指状片段与一个7-bp的序列结合，其共有序列为5‘ANAAGGT3’。计算机搜索表明，SET结构域可能与组蛋白H3赖氨酸残基的甲基酶活性有关。提示MFBA蛋白可能是一种染色质重塑蛋白。较少

Fruiting-body formation of basidiomycetes is one of the most typical and attractive morphological differentiation observed in microorganisms. To understand the molecular mechanisms of fruiting-body formation in Lentinula edodes (Shiitake), we have studied on the target genes of two DNA-binding transcription factors PRIB and Le.CDC5, both of which regulate the fruiting-body formation. The PRIB protein binds to a 16-bp sequence with the consensus sequence of 5'GGGGGGGACAGGANCC3' and the Le.CDC5 protein binds to a 7-bp sequence with theconsensus sequence 5'GCAATGT3'. MfbA is also interesting protein that regulates the fruiting-body formation and possesses RGD sequence, PHD finger and SET domain. So we studied properties of MfbA protein. Concerning the PRIB, Le.CDC5 and MfbA, we obtained the following results. (1)The three target genes were identified for PRIB protein, ie., priB, uck1 (UMP-CMP kinase genes) and mfbC, the homologue of Saccharomyces cerevisiae YJRO070c. The mfbC gene is cons … More idered to encode the protein interacting to a putative translation initiation factor eIF5A. Only mature fruiting body was shown to contain the transcript of the mfbC gene almost exclusively, suggesting that mfbC may play a role at the final stage of fruiting-body formation. The mfbC transcript showed a region-specific distribution in hymenophore (gill tissue). High level of the mfbC transcript was detected in the outer region of trama, which is the region branching out into subhymenium. (2)We isolated two (3.7-kb and 3.9-kb) genomic HindIII fragments, to which Le.CDC5 protein binds. The two fragments contained several 7-bp consensus-like sequences and Le.CDC5 protein bound to them. They contained two or three genes of which functions were unknown. (3)The PHD finger-containing fragment of MFBA protein was found to bind to a 7-bp sequence with the consensus sequence of 5'ANAAGGT3'. Computer searching gave the information that the SET domain may be related to the methylase activity for the lysine residues of histone H3. These imply the possibility that MFBA protein may be a sort of chromatin-remodelling protein. Less