THE REALTION BETWEEN HETEROCHROMATIN AND W CHROMOSOME OF THE SILKWORM,BOMBYX MORI

家蚕和鳜鱼的性染色体公式为雌性为ZW (XY)，雄性为ZZ。采用聚合酶链反应（PCR）方法，用700个任意10-mer引物对家蚕、家蚕和中国家蚕的雌雄基因组dna进行了比较。发现了4个雌性特异性rapd （W-Kabuki, W-Samurai， W-Kamikaze和W-Yamato）。这四个女性特有的rapd被认为来自W染色体，因为其他染色体是两性共有的。计算机检索这4个rapd的氨基酸序列，发现它们都与先前报道的各种生物中已知的反转录转座元件编码的氨基酸序列同源。为了进一步分析家蚕的W染色体，我们构建了基因组DNA lambda噬菌体文库，并采用PCR策略筛选了含有W- kabuki RAPD序列的lambda噬菌体克隆。然后对18.1 kb的DNA插入片段进行测序。基于计算机搜索，我们确定这18.1 kb的插入DNA主要由三个反转录转座元件，一个反转录子和一个功能未知的插入组成。每个元件，即一个非LTR逆转录转座元件BMC1，一个反转录子Bm1，功能未知的插入DNA，和一个新的类似复制体的LTR逆转录转座元件Yakozuna，被插入到一个新的类似吉普西- ty3的LTR逆转录转座元件Kabuki中。横纲包含一个长开放阅读框（ORE），整个推断的ORF氨基酸序列与果蝇拷贝体具有很强的同源性。该BMC1全长5091 bp，包含一个5‘未翻译区、两个完整的orf和以poly (a)尾终止的3’-UTR。与常染色体和Z染色体相比，家蚕和鳜鱼在W染色体上可能积累了更多的反转录转座因子和衍生物。

The sex chromosome formulas of Bombyx mori and B.mandarina are ZW (XY) for the female and ZZ for the male. Genomic DNAs were compared between males and females of the silkworm, B.mori and B.mandarina by polymerase chain reaction (PCR) with 700 arbitrary 10-mer primers. Four female-specific RAPDs (W-Kabuki, W-Samurai, W-Kamikaze, and W-Yamato) were found. The four female-specific RAPDs are assumed tobe derived from the W chromosome because the other chromosomes are shared by both sexes. A computer search for deduced amino acid sequences of these four RAPDs revealed that all of them showed homology to previously reported amino acid sequences encoded in known retrotransposable elements from various organisms. To further analyze the W chromosome of B.mori we constructed a genomic DNA lambda phage library and picked the lambda phage clone containing the W-Kabuki RAPD sequence by using a PCR strategy. We then sequenced the 18.1-kb DNA inset. Based on a computer search, we determined that this 18.1-kb insertional DNA is composed primarily of clusters of three retrotransposable elements, one retroposon, and one functionally unknown insertion. Each element, namely a non-LTR retrotransposable element BMC1, a retroposon Bm1, functionally unknown inserted DNA, and a novel copia-like LTR retrotransposable element, Yakozuna, was inserted into a novel gypsy-Ty3-like LTR retrotransposable element, Kabuki. Yokozuna contains a single long open reading frame (ORE) and the whole deduced amino acid sequence of ORF reveals strong homology with copia of Drosophila. This BMC1 is 5091 bp and contains a 5'untranslated region, two intact ORFs, and 3'-UTR which terminates in a poly (A) tail. In B.mori and B.mandarina many retrotransposable elements and derivatives might be accumulated in W chromosome than in autosomes or Z chromosome.