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

家蚕和家蚕B性染色体公式为：雌性为ZW（XY），雄性为ZZ。用700个10-mer随机引物进行聚合酶链反应（PCR），比较了家蚕（B.mori）和家蚕（B. mori）雌雄个体基因组DNA的差异。发现了4个女性特有的RAPD（W-Kabuki、W-Samurai、W-Kamikaze和W-Yamato），这4个女性特有的RAPD被认为是来自W染色体，因为其他染色体是两性共有的。计算机搜索推导的氨基酸序列，这四个RAPDs显示，所有这些都显示出同源性，以前报道的氨基酸序列编码的已知反转录转座因子从各种生物。为了进一步分析家蚕B的W染色体，我们构建了家蚕基因组DNA λ噬菌体文库，并通过PCR策略筛选出含有W-歌舞伎RAPD序列的λ噬菌体克隆。然后我们对18.1-kb DNA插入序列进行测序。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因子，一个反转录子，和一个功能未知的插入簇组成。每个元件，即非LTR逆转录转座因子BMC 1、逆转座子Bm 1、功能未知的插入DNA和新型copia样LTR逆转录转座因子Yakozuna，被插入到新型gypsy-Ty 3样LTR逆转录转座因子Kabuki中。Yokozuna含有一个长的开放阅读框架（ORE），其ORF的氨基酸序列与果蝇的copia有很强的同源性。BMC 1全长5091 bp，包含一个5 '端非翻译区、两个完整的ORF和一个终止于poly（A）尾的3'端非翻译区。在B和B中，反转录转座因子及其衍生物在W染色体上的积累可能多于常染色体或Z染色体。

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.