The promoter and transcribed regions of the Leishmania tarentolae spliced leader RNA gene array are devoid of nucleosomes.
The promoter and transcribed regions of the Leishmania tarentolae spliced leader RNA gene array are devoid of nucleosomes.
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DOI：
10.1186/1471-2180-7-44
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发表时间：
2007-05-22
期刊：
影响因子：
4.2
通讯作者：
Sturm NR
中科院分区：
文献类型：
--
作者：
Hitchcock RA;Thomas S;Campbell DA;Sturm NR
剪接前导(SL)RNA为动质体内的所有核mRNAs提供5‘m7G帽和前39个核苷酸。这种小的核RNA是由RNA聚合酶II从单个启动子转录而来的。在塔伦托利什曼原虫中，SL RNA基因位于两个多拷贝串联阵列中，分别命名为MINA和MINB。SL启动子在药物选择、外体SL RNA基因盒PX-TSL上的转录积累量约为未克隆转染体中基因组阵列的10%。这种差异与序列或拷贝数无关，因此可能是由于表观遗传因素干扰了SL启动子的功能。为了探索这些可能性，我们研究了SL RNA基因的核质定位以及它们的核小体结构。基因组SL RNA基因和Episome没有在细胞核内共定位。每个基因组重复序列包含一个位于非转录基因间隔区的核小体。由于核小体的结合，363-bp的MINA阵列对微球菌核酸酶在相对于转录起始点的-258到-72位之间的消化具有抵抗力，从而使启动子元件和整个转录区域暴露在蛋白质相互作用中。观察到~164bp保护片段的模式，对应于通常由核小体结合的DNA的量。相比之下，PX-TSL Episome上的核小体随机分布在外体SL盒上，使转录因子进入外体启动子的途径减少了约74%。Episome转染体的克隆揭示了一系列转录活性，暗示了一种表观遗传机制。在给定的寄生虫中，大约25%的时间，PX Episome上的无序核小体处于允许转录SL RNA盒的构象中。核小体干扰可能是SL RNA基因盒明显转录抑制的主要因素。再加上驱动可选药物标记表达的跑动式转录的要求，由于次优的核质定位和起始复合体的破坏，外体SL的转录可能会进一步减少。
The spliced leader (SL) RNA provides the 5' m7G cap and first 39 nt for all nuclear mRNAs in kinetoplastids. This small nuclear RNA is transcribed by RNA polymerase II from individual promoters. In Leishmania tarentolae the SL RNA genes reside in two multi-copy tandem arrays designated MINA and MINB. The transcript accumulation from the SL promoter on the drug-selected, episomal SL RNA gene cassette pX-tSL is ~10% that of the genomic array in uncloned L. tarentolae transfectants. This disparity is neither sequence- nor copy-number related, and thus may be due to interference of SL promoter function by epigenetic factors. To explore these possibilities we examined the nucleoplasmic localization of the SL RNA genes as well as their nucleosomal architecture. The genomic SL RNA genes and the episome did not co-localize within the nucleus. Each genomic repeat contains one nucleosome regularly positioned within the non-transcribed intergenic region. The 363-bp MINA array was resistant to micrococcal nuclease digestion between the -258 and -72 positions relative to the transcription start point due to nucleosome association, leaving the promoter elements and the entire transcribed region exposed for protein interactions. A pattern of ~164-bp protected segments was observed, corresponding to the amount of DNA typically bound by a nucleosome. By contrast, nucleosomes on the pX-tSL episome were randomly distributed over the episomal SL cassette, reducing transcription factor access to the episomal promoter by approximately 74%. Cloning of the episome transfectants revealed a range of transcriptional activities, implicating a mechanism of epigenetic heredity. The disorganized nucleosomes on the pX episome are in a permissive conformation for transcription of the SL RNA cassette approximately 25% of the time within a given parasite. Nucleosome interference is likely the major factor in the apparent transcriptional repression of the SL RNA gene cassette. Coupled with the requirement for run-around transcription that drives expression of the selectable drug marker, transcription of the episomal SL may be reduced even further due to sub-optimal nucleoplasmic localization and initiation complex disruption.
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影响因子：
1.5
作者：
Gunzl, A;Ullu, E;Tschudi, C
通讯作者：
Tschudi, C
影响因子：
1.5
作者：
CROZATIER, M;DEBRIJ, RJ;BORST, P
通讯作者：
BORST, P
影响因子：
11.4
作者：
HAN, M;KIM, UJ;GRUNSTEIN, M
通讯作者：
GRUNSTEIN, M
影响因子：
11.4
作者：
Moreira, JMA;Holmberg, S
通讯作者：
Holmberg, S
影响因子：
--
作者：
Palenchar, JB;Liu, WZ;Bellofatto, V
通讯作者：
Bellofatto, V