Moshkin Y M, Alekseyenko A A, Semeshin V F, Spierer A, Spierer P, Makarevich G F, Belyaeva E S, Zhimulev I F
Institute of Cytology and Genetics, Siberian Division of Russian Academy of Sciences, Novosibirsk 630090, Russia.
Proc Natl Acad Sci U S A. 2001 Jan 16;98(2):570-4. doi: 10.1073/pnas.98.2.570. Epub 2001 Jan 2.
The level of polyteny of the Drosophila salivary gland chromosomes was determined throughout the chromosome region 89E1-4, the locus of the Bithorax Complex. A zone of underreplication spans the 300 kb of DNA from the Ubx to Abd-B loci. From the centromere proximal end of the complex, a 70-kb-long gradual decrease of polytenization starts with the Ubx transcription unit and, after a floor corresponding to the abd-A locus, raises gradually back to the maximum over 70 kb in the region of the Abd-B transcription unit. In flies carrying the mutation Suppressor of DNA Underreplication [Su(UR)ES], the underreplication of the Bithorax Complex is fully suppressed. In the wild type, the Bithorax Complex forms a weak point featuring thinner bands separated by clefts or constrictions. In Su(UR)ES strain in contrast, the 89E1-4 band looks like a single solid band consisting of homogenous dense material. We speculate that the wild-type Su(UR)ES protein hampers DNA replication of silenced domains and leads to their underreplication in salivary gland polytene chromosomes.
测定了果蝇唾液腺染色体在整个89E1 - 4染色体区域（双胸复合体的基因座）的多线化水平。一个复制不足区域跨越了从超双胸（Ubx）基因座到腹部B（Abd - B）基因座的300 kb DNA。从复合体的着丝粒近端开始，一个70 kb长的多线化逐渐减少过程始于Ubx转录单元，在对应于腹部A（abd - A）基因座的一个平台期之后，在Abd - B转录单元区域内又逐渐回升至70 kb以上的最大值。在携带DNA复制不足抑制因子[Su(UR)ES]突变的果蝇中，双胸复合体的复制不足被完全抑制。在野生型果蝇中，双胸复合体形成一个弱点，其特征是有较细的带，这些带被裂缝或缢缩隔开。相比之下，在Su(UR)ES品系中，89E1 - 4带看起来像一条由均匀致密物质组成的单一连续带。我们推测，野生型Su(UR)ES蛋白阻碍了沉默结构域的DNA复制，并导致其在唾液腺多线染色体中的复制不足。
