Lohe A R, Hilliker A J, Roberts P A
Department of Genetics, Washington University School of Medicine, St. Louis, Missouri 63110.
Genetics. 1993 Aug;134(4):1149-74. doi: 10.1093/genetics/134.4.1149.
Heterochromatin in Drosophila has unusual genetic, cytological and molecular properties. Highly repeated DNA sequences (satellites) are the principal component of heterochromatin. Using probes from cloned satellites, we have constructed a chromosome map of 10 highly repeated, simple DNA sequences in heterochromatin of mitotic chromosomes of Drosophila melanogaster. Despite extensive sequence homology among some satellites, chromosomal locations could be distinguished by stringent in situ hybridizations for each satellite. Only two of the localizations previously determined using gradient-purified bulk satellite probes are correct. Eight new satellite localizations are presented, providing a megabase-level chromosome map of one-quarter of the genome. Five major satellites each exhibit a multi-chromosome distribution, and five minor satellites hybridize to single sites on the Y chromosome. Satellites closely related in sequence are often located near one another on the same chromosome. About 80% of Y chromosome DNA is composed of nine simple repeated sequences, in particular (AAGAC)n (8 Mb), (AAGAG)n (7 Mb) and (AATAT)n (6 Mb). Similarly, more than 70% of the DNA in chromosome 2 heterochromatin is composed of five simple repeated sequences. We have also generated a high resolution map of satellites in chromosome 2 heterochromatin, using a series of translocation chromosomes whose breakpoints in heterochromatin were ordered by N-banding. Finally, staining and banding patterns of heterochromatic regions are correlated with the locations of specific repeated DNA sequences. The basis for the cytochemical heterogeneity in banding appears to depend exclusively on the different satellite DNAs present in heterochromatin.
果蝇中的异染色质具有不同寻常的遗传、细胞学和分子特性。高度重复的DNA序列（卫星DNA）是异染色质的主要成分。利用克隆卫星DNA的探针，我们构建了黑腹果蝇有丝分裂染色体异染色质中10个高度重复的简单DNA序列的染色体图谱。尽管一些卫星DNA之间存在广泛的序列同源性，但通过对每个卫星DNA进行严格的原位杂交，可以区分染色体位置。以前使用梯度纯化的大量卫星DNA探针确定的定位中只有两个是正确的。本文给出了8个新的卫星DNA定位，提供了基因组四分之一的兆碱基水平染色体图谱。5个主要卫星DNA各自呈现多染色体分布，5个次要卫星DNA与Y染色体上的单个位点杂交。序列密切相关的卫星DNA通常位于同一染色体上彼此相邻的位置。Y染色体DNA约80%由9个简单重复序列组成，特别是（AAGAC）n（8兆碱基）、（AAGAG）n（7兆碱基）和（AATAT）n（6兆碱基）。同样，2号染色体异染色质中70%以上的DNA由5个简单重复序列组成。我们还利用一系列易位染色体构建了2号染色体异染色质中卫星DNA的高分辨率图谱，这些易位染色体在异染色质中的断点通过N带进行了排序。最后，异染色质区域的染色和带型与特定重复DNA序列的位置相关。带型中细胞化学异质性的基础似乎完全取决于异染色质中存在的不同卫星DNA。
