Mok E H, Smith H S, DiBartolomeis S M, Kerrebrock A W, Rothschild L J, Lange T S, Gerbi S A
Brown University Division of Biology and Medicine, Providence, RI 02912, USA.
Chromosoma. 2001 Jul;110(3):186-96. doi: 10.1007/s004120000119.
The maintenance of the expanded state of DNA puffs II/2B and II/9A in polytene chromosomes from stage 14 x 7 Sciara coprophila salivary glands was assayed after inhibition of RNA synthesis, DNA synthesis, or both processes together. Heat shock conditions were established in order to inhibit transcription. Polypeptides of Mr 72,000 and 36,000 were produced in Sciara after heat shock. The gene encoding the Mr 72,000 polypeptide, the homolog of Drosophila hsp70, was cloned. In situ hybridization detected Sciara hsp70 at bands 4A and 17C on chromosome IV. Sciara hsp70 encodes a 2.3 kb heat shock mRNA. DNA puffs (e.g., DNA puffs 2B and 9A on chromosome II) remained fully expanded even after inhibition of transcription by heat shock or actinomycin D, or after inhibition of DNA replication by aphidicolin, or inhibition of both RNA synthesis and DNA synthesis together by actinomycin D plus aphidicolin. Therefore, maintenance of the DNA puff expanded state in Sciara does not require ongoing transcription and/or replication. Mechanisms for initiation and for maintenance of puffs (open chromatin structure) are discussed.
在抑制RNA合成、DNA合成或同时抑制这两个过程后，检测了来自14×7阶段嗜粪Sciara唾液腺的多线染色体中DNA泡II/2B和II/9A的扩展状态的维持情况。建立热休克条件以抑制转录。热休克后，Sciara产生了分子量为72,000和36,000的多肽。编码分子量为72,000多肽（果蝇hsp70的同源物）的基因被克隆。原位杂交在第四条染色体的4A和17C带检测到Sciara hsp70。Sciara hsp70编码一个2.3 kb的热休克mRNA。即使在通过热休克或放线菌素D抑制转录后，或在通过阿非迪霉素抑制DNA复制后，或在通过放线菌素D加阿非迪霉素同时抑制RNA合成和DNA合成后，DNA泡（例如，第二条染色体上的DNA泡2B和9A）仍保持完全扩展状态。因此，Sciara中DNA泡扩展状态的维持不需要正在进行的转录和/或复制。本文讨论了泡（开放染色质结构）起始和维持的机制。
