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

家蚕和野桑蚕的性染色体公式为雌性为ZW(XY)，雄性为ZZ。用700个随机10聚体引物对家蚕、野桑蚕和野桑蚕的雌雄基因组DNA进行了比较分析。发现了四种女性特有的RAPD(W-歌舞伎、W-武士、W-神风和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享的。对这四个RAPD的推导氨基酸序列的计算机搜索显示，它们都与以前报道的氨基酸序列同源，这些氨基酸序列编码在各种生物的已知逆转座子中。为了进一步对家蚕W染色体进行分析，我们构建了家蚕基因组DNA Lambda噬菌体文库，并采用聚合酶链式反应的方法筛选到了含有W-Kabuki随机扩增序列的Lambda噬菌体克隆。然后，我们对18.1kb的DNA插入物进行了测序。基于计算机搜索，我们确定这个18.1kb的插入DNA主要由三个反转录转座元件组成的簇，一个反转录转座子，一个功能未知的插入。将每个元件，即一个非LTR逆转座子Bm1，一个功能未知的插入DNA的逆转录子Bm1，以及一个新的拷贝样LTR逆转座子元件Yakozina，插入到一个新的吉普赛-Ty3样LTR逆转座子元件Kabuki中。Yokozina含有一个长的开放阅读框架(ORE)，其推导的氨基酸序列与果蝇Copia有很强的同源性。该BMC1全长5091个碱基，含有一个5‘非翻译区、两个完整的ORF和3’-非编码区，终止于PolyA尾部。在家蚕和野桑蚕中，W染色体可能比常染色体或Z染色体中积累了更多的逆转座子及其衍生物。

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.