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的不同，因为成熟的mrna是通过大的多顺反子初级转录物的传递产生的。此外，没有证据表明基因表达的转录调节通常在其他生物体中看到。我们实验室之前的工作表明，转录仅在同一DNA链上相邻蛋白质编码基因的大（50-500 kb）不同簇之间的少数位点开始，并且在趋同基因簇之间的连接处终止之前进行双向转录。然而，参与转录灌注的“启动子”元素仍然是一个谜。在其他真核生物中，组蛋白修饰和染色质重塑对转录激活很重要，最近的实验表明，这可能也是锥虫的情况。这使我们假设，不同PGCs之间的链开关区域招募染色质重改造复合物，这些复合物修饰组蛋白并改变这些区域的局部染色质结构，从而允许RNA聚合酶II预起始复合物进入，然后在两个方向上启动转录。在本提案中，我们将验证这一假设，并在我们目前工作的基础上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.