Fournier A, Taneja R, Gopalkrishnan R, Prudhomme J C, Gopinathan K P
Centre de Génétique Moléculaire et Cellulaire, University Claude Bernard Lyon 1, Villeurbanne, France.
Gene. 1993 Dec 8;134(2):183-90. doi: 10.1016/0378-1119(93)90092-h.
Ten different tRNA(Gly1) genes from the silk worm, Bombyx mori, have been cloned and characterized. These genes were transcribed in vitro in homologous nuclear extracts from the posterior silk gland (PSG) or nuclear extracts derived from the middle silk gland or ovarian tissues. Although the transcription levels were much higher in the PSG nuclear extracts, the transcriptional efficiency of the individual genes followed a similar pattern in all the extracts. Based on the levels of in vitro transcription, the ten tRNA(Gly1) genes could be divided into three groups, viz., those which were transcribed at very high levels (e.g., clone pR8), high to medium levels (e.g., pBmi1, pBmp1, pBmh1, pBmt1) and low to barely detectable levels (e.g., pBms1, pBmj1 and pBmk1). The coding sequences of all these tRNA genes being identical, the differential transcription suggested that the flanking sequences modulate their transcriptional efficiency. The presence of positive and negative regulatory elements in the 5' flanking regions of these genes was confirmed by transcription competition experiments. A positive element was present in the immediate upstream A+T-rich sequences in all the genes, but no consensus sequences correlating to the transcriptional status could be generated. The presence of negative elements on the other hand was indicated only in some of the genes and therefore may have a role in the differential transcription of these tRNA(Gly1) genes in vivo.
家蚕（Bombyx mori）的10个不同的tRNA（Gly1）基因已被克隆并进行了特征分析。这些基因在来自后部丝腺（PSG）的同源核提取物或来自中部丝腺或卵巢组织的核提取物中进行体外转录。尽管在PSG核提取物中转录水平要高得多，但各个基因的转录效率在所有提取物中遵循相似的模式。根据体外转录水平，这10个tRNA（Gly1）基因可分为三组，即转录水平非常高的（例如克隆pR8）、高到中等水平的（例如pBmi1、pBmp1、pBmh1、pBmt1）和低到几乎检测不到水平的（例如pBms1、pBmj1和pBmk1）。所有这些tRNA基因的编码序列相同，差异转录表明侧翼序列调节它们的转录效率。转录竞争实验证实了这些基因5'侧翼区域中正负调控元件的存在。所有基因紧邻上游富含A + T的序列中都存在一个正调控元件，但无法生成与转录状态相关的共有序列。另一方面，仅在一些基因中发现了负调控元件，因此它们可能在体内这些tRNA（Gly1）基因的差异转录中起作用。
