Nelson L G, Daneholt B
Chromosoma. 1981;83(5):645-59. doi: 10.1007/BF00328524.
Galactose has been used as a tool to modify gene activity in the giant puffs Balbiani ring 2 (BR2) and Balbiani ring 1 (BR1) on chromosome IV in the salivary glands of Chironomus tentans. BR2 decreased gradually and was absent or almost absent after a four day galactose treatment. Concomitant with this morphological change, the labelling of the population of growing 75S RNA molecules in BR2 decreased, and was essentially abolished after four days in galactose. Since the elongation rate at the 75S RNA genes proved to be the same in the galactose treated glands as in the control glands, the decreased labelling in BR2 was likely to correspond to a decreased production of 75S RNA. No changes in the size distribution of the growing 75S RNA molecules were noted during the galactose treatment, suggesting that the modulation of the activity was most likely accomplished at the initiation level, but regulation of a very early premature termination could not be excluded. When galactose was removed from the medium, BR2 attained its normal size and its ordinary RNA labelling. BR1 was studied in parallel with BR2 and it behaved strikingly different: BR1 expanded during the galactose treatment and the amount of growing 75S RNA increased, indicating an enhanced production of this 75S RNA species. Also the modulation of BR1 RNA synthesis was reversible. During the galactose treatment no changes in the labelling of chromosome I-III and of nucleolar RNA were observed suggesting that during the four day treatment, galactose exerted its effect mainly on the synthesis of BR2 and BR1 transcription products. The significance of these observations are considered in relation to the information available on the synthesis of the corresponding secretory polypeptides and the formation of the tube-like burrows. We also discuss the implications of the results for models of the regulation of gene activity and of the puffing process.
半乳糖已被用作一种工具，用于改变摇蚊唾液腺中第四条染色体上的巨大胀泡巴尔比亚尼环2（BR2）和巴尔比亚尼环1（BR1）中的基因活性。经过四天的半乳糖处理后，BR2逐渐缩小，直至消失或几乎消失。伴随着这种形态变化，BR2中正在生长的75S RNA分子群体的标记减少，在半乳糖中处理四天后基本消失。由于在半乳糖处理的腺体中，75S RNA基因的延伸速率与对照腺体中的相同，因此BR2中标记的减少可能对应于75S RNA产量的降低。在半乳糖处理期间，未观察到正在生长的75S RNA分子的大小分布发生变化，这表明活性的调节很可能是在起始水平完成的，但不能排除对非常早期的过早终止进行调节的可能性。当从培养基中去除半乳糖时，BR2恢复到正常大小并恢复其正常的RNA标记。BR1与BR2同时进行研究，其表现出显著不同：在半乳糖处理期间，BR1膨胀，正在生长的75S RNA数量增加，表明这种75S RNA种类的产量增加。BR1 RNA合成的调节也是可逆的。在半乳糖处理期间，未观察到第一至第三条染色体和核仁RNA标记的变化，这表明在四天的处理过程中，半乳糖主要对BR2和BR1转录产物的合成产生影响。结合有关相应分泌多肽合成和管状洞穴形成的现有信息，考虑了这些观察结果的意义。我们还讨论了这些结果对基因活性调节模型和胀泡过程模型的影响。
