Transcription of Protein-coding Genes in Leishmania

尽管经过了20多年的分子研究。目前对利什曼原虫和其他锥虫的蛋白质编码基因转录的基本过程知之甚少，除了它与其他真核生物不同，因为成熟的mRNA是通过大的多顺反子初级转录本的转译产生的。此外，没有证据表明fO（通常在其他生物体中看到的基因表达的转录调节）。我们实验室以前的工作已经表明，转录起始于同一DNA链上相邻蛋白质编码基因的大的（50-500 kb）发散簇之间的少数位点，并在会聚基因簇之间的连接处的温度升高之前双向进行。然而，参与转录起始的“启动子”元件仍然是一个谜。在其他真核生物中，组蛋白修饰和染色质重塑对于转录的激活是重要的，最近的实验表明，这可能也是锥虫的情况。这促使我们假设，不同PGC之间的链转换区域招募染色质重塑复合物，这些复合物修饰组蛋白并改变这些区域中的局部染色质结构，以允许RNA聚合酶II前起始复合物进入，然后启动两个方向的转录。在这个建议中，我们将测试这一假设，并建立在我们目前的工作，以进一步表征参与转录起始的染色质修饰酶。

Despite more than 20 years of molecular investigation. little is currently known about the essential process of the transcriptioo of protein-coding genes in Leishmania and other trypanosomatids, other than that it differs from that in other eukaryotes because mature mRNAs are generated by transspncing of large polycistronic primary transcripts. Moreover, there is no evidence fO( the transcriptional regulation of gene expression typically seen in other organisms. Previous worK from our laboratory has shown that transcription initiates at ooly a small number of sites between large (50-500 kb) divergent clusters of adjacent protein-coding genes on the same DNA strand and proceeds bi-directionally before temlination at the junction between convergent gene clusters. However, the 'promoter" elements involved in transcription inillation remain a mystery. In other eukaryotes, histone modification and chromatin re-modeling are important for activation of transcription, and recent experiments suggest that this may also be the case in trypanosomatids. This has ted us to hypothesize that the strand-switch regions between divergent PGCs recruit chromatin-remodenng complexes which modify histones and alter the local chromatin structure in these regions to allow access by the RNA polymerase II preinitiation complex, which then initiates transcription in both directions. In this proposal, we will test this hypothesis and build on our current work to further characterize the chromatin-modifying enzymes that are involved in transcription initiation.