Ugarković D, Plohl M, Petitpierre E, Lucijanić-Justić V, Juan C
Department of Molecular Genetics, Ruder Bosković Institute, Zagreb, Croatia.
Chromosome Res. 1994 May;2(3):217-23. doi: 10.1007/BF01553322.
Satellite DNA from the mealworm beetle, Tenebrio obscurus, is composed of 344 bp long monomers of high AT content (68%), and represents 15% of the total DNA. In situ hybridization reveals the positions of the satellite on the pericentromeric heterochromatin of all T. obscurus chromosomes. To compare restriction enzyme (RE) effects with those on naked DNA, fixed chromosomes were digested with REs having recognition sites in most of the satellite monomers, and also with enzymes having target sites present only partially, or very rarely in the satellite units. All enzymes produce similar C-like banding patterns showing heterochromatin resistance to digestion regardless of the enzyme used. In situ nick translation suggests the inability of REs to cleave satellite DNA rather than the inefficient extraction of DNA fragments. DNA in heterochromatin was only extensively digested when the chromosomes were preincubated with proteinase K, indicating that accessibility of REs to DNA is increased by the removal of chromosomal proteins. This is in contrast to recently obtained results in Tenebrio molitor, where cleavage of satellite DNA is equally efficient in both fixed chromosomes and in naked DNA. The satellite DNAs of the two congeneric species differ in their AT content, and their primary and higher order structure, which could influence both heterochromatin structure and the accessibility of REs to satellite DNA.
黄粉虫（Tenebrio obscurus）的卫星DNA由长度为344 bp的高AT含量（68%）单体组成，占总DNA的15%。原位杂交揭示了卫星在所有黄粉虫染色体着丝粒周围异染色质上的位置。为了比较限制酶（RE）对固定染色体的作用与对裸露DNA的作用，用在大多数卫星单体中具有识别位点的限制酶，以及仅在卫星单元中部分存在或非常罕见地存在靶位点的酶对固定染色体进行消化。无论使用何种酶，所有酶都产生相似的C类带型，表明异染色质对消化具有抗性。原位缺口平移表明限制酶无法切割卫星DNA，而不是DNA片段提取效率低下。只有当染色体用蛋白酶K预孵育时，异染色质中的DNA才会被广泛消化，这表明去除染色体蛋白可增加限制酶对DNA的可及性。这与最近在黄粉虫（Tenebrio molitor）中获得的结果相反，在黄粉虫中，卫星DNA在固定染色体和裸露DNA中的切割效率相同。这两个同属物种的卫星DNA在AT含量、一级和高级结构上存在差异，这可能会影响异染色质结构以及限制酶对卫星DNA的可及性。
