classII transposon 是隨機的嗎？

在美在我的帖子里問到有關class II transposon 是否是隨機的。由於我對classII 一無所知，當時並沒有回答。今天剛好讀到一篇發表在PNAS 上的文章，拿到這裡與大家共享。

Proc. Natl. Acad. Sci. USA
Vol. 92, pp. 3804-3808, April 1995

Transposable elements are stable structural components of
Drosophila melanogaster heterochromatinS. PIMPINELLI*, M. BERLOCOt, L. FANTit, P. DIMITRI*, S. BONACCORSI*t, E. MARCHETTI*, R. CAIZZIt,
C. CAGGESEt, AND M. GATrrI*t
*Istituto Pasteur-Fondazione Cenci Bolognetti and *Centro di Genetica Evoluzionistica del Consiglio Nazionale delle Ricerche, Dipartimento di Genetica e
Biologia Molecolare, Universita di Roma "La Sapienza," P.le A. Moro 5, 00185 Rome, Italy; and tIstituto di Genetica, Universita' di Bari, via
Amendola 165a, 00176 Bari, Italy
Communicated by Dan L. Lindsley, University of California, San Diego, La Jolla, CA,

[ 本帖最後由 研究 於 2007-9-22 04:59 編輯 ]

這篇文章中作者用了11個不同的transposon 檢測transposon 的作用。結果證明，無論是classI 還是class II ,都需要嚴格的序列要求，而不是隨機的。

[ 本帖最後由 研究 於 2007-9-22 02:18 編輯 ]

Class I elements are further subdivided into retrotransposons and retroposons (2).

Retrotransposons (e.g., copia, gypsy, mdg-1,and blood) have direct long terminal repeats (LTRs) and contain sequences with significant homology to both the retroviralpol gene, which encodes a reverse transcriptase, and the viral gag polyprotein (1-3).
Retroposons（在美問的non-LTR retrotransposon) (e.g., I, F, G, and Doc) also encode putative reverse transcriptase and gag-like proteins but have no terminal repeats and carry a characteristic A-rich sequence at their 3' ends (1-3).

Class II elements, which transpose directly from DNA to DNA, are also subdivided into two subclasses (2).

The TEs of the first subclass (e.g., P, hobo, and Bari-1) are characterized by the presence of short inverted repeats at their termini and encode a transposase which is required for their own transposition (1-4).

The second subclass includes only thefold-back elements, which contain heterogeneous central portions flanked by long terminal inverted repeats (1-3).

[ 本帖最後由 研究 於 2007-9-22 02:43 編輯 ]

Yeah! Give me five!

原帖由 aawang 於 2007-9-22 02:18 發表
Yeah! Give me five!

yes!

認定「進化論」的也同樣是憑著信心，而不是眼見的證據的。「在美一方」，「blackcurtain」， 「confuse」，對不對？

實在來說，連你請朋友到街上飯館吃一頓，也得憑信心，不憑眼見的：你怎能保證食品衛生，沒人下毒？也沒見誰帶著檢測劑請人吃飯的。

看來信心還是恆重要的。不然假始祖鳥怎麼能上美國國家地里雜誌？

周末愉快！