Locke J, Podemski L, Roy K, Pilgrim D, Hodgetts R
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
Genome Res. 1999 Feb;9(2):137-49.
Chromosome 4 from Drosophila melanogaster has several unusual features that distinguish it from the other chromosomes. These include a diffuse appearance in salivary gland polytene chromosomes, an absence of recombination, and the variegated expression of P-element transgenes. As part of a larger project to understand these properties, we are assembling a physical map of this chromosome. Here we report the sequence of two cosmids representing approximately 5% of the polytenized region. Both cosmid clones contain numerous repeated DNA sequences, as identified by cross hybridization with labeled genomic DNA, BLAST searches, and dot matrix analysis, which are positioned between and within the transcribed sequences. The repetitive sequences include three copies of the mobile element Hoppel, one copy of the mobile element HB, and 18 DINE repeats. DINE is a novel, short repeated sequence dispersed throughout both cosmid sequences. One cosmid includes the previously described cubitus interruptus (ci) gene and two new genes: that a gene with a predicted amino acid sequence similar to ribosomal protein S3a which is consistent with the Minute(4)101 locus thought to be in the region, and a novel member of the protein family that includes plexin and met-hepatocyte growth factor receptor. The other cosmid contains only the two short 5'-most exons from the zinc-finger-homolog-2 (zfh-2) gene. This is the first extensive sequence analysis of noncoding DNA from chromosome 4. The distribution of the various repeats suggests its organization is similar to the beta-heterochromatic regions near the base of the major chromosome arms. Such a pattern may account for the diffuse banding of the polytene chromosome 4 and the variegation of many P-element transgenes on the chromosome.
黑腹果蝇的4号染色体有几个不同寻常的特征，使其有别于其他染色体。这些特征包括在唾液腺多线染色体上呈现弥散外观、缺乏重组以及P元件转基因的斑驳表达。作为了解这些特性的一个更大项目的一部分，我们正在构建该染色体的物理图谱。在此，我们报告了两个黏粒的序列，它们代表了多线化区域的约5%。通过与标记的基因组DNA进行交叉杂交、BLAST搜索和点阵分析鉴定，两个黏粒克隆都包含大量重复DNA序列，这些序列位于转录序列之间和内部。重复序列包括三个移动元件Hoppel拷贝、一个移动元件HB拷贝和18个DINE重复序列。DINE是一种新颖的短重复序列，分散在两个黏粒序列中。一个黏粒包含先前描述的肘脉中断（ci）基因和两个新基因：一个预测氨基酸序列与核糖体蛋白S3a相似的基因，这与认为位于该区域的Minute(4)101位点一致，以及一个包含丛状蛋白和肝细胞生长因子受体的蛋白家族的新成员。另一个黏粒仅包含锌指同源物2（zfh - 2）基因的两个最靠近上游的短外显子。这是对4号染色体非编码DNA的首次广泛序列分析。各种重复序列的分布表明其组织方式类似于主要染色体臂基部附近的β异染色质区域。这样的模式可能解释了多线4号染色体的弥散带型以及该染色体上许多P元件转基因的斑驳现象。
