Britten R J, McCormack T J, Mears T L, Davidson E H
Division of Biology, California Institute of Technology, Corona del Mar 92625.
J Mol Evol. 1995 Jan;40(1):13-24. doi: 10.1007/BF00166592.
Eight new examples of retrotransposons of the Gypsy/Ty3 class have been identified in marine species. A 525-nt pol gene-coding region was amplified using degenerate primers from highly conserved regions and has extended the range of recognition of Gypsy/Ty3 far beyond those previously known. The following matrix shows the percentage AA divergence of the translations of this segment of the pol gene coding region. [table: see text] The underlines separate three groups of retrotransposons that can be recognized on the basis of this amino acid sequence. The new upper group shows surprising amino acid sequence similarity among members from the DNA of herring, sea urchin, starfish, and a tunicate. For example, the herring element differs by only 41% from the Ciona element and 46% from the sea urchin element. The group between the lines includes members close to previously known elements (marked by asterisks) and has so far been found only in sea urchins. The two upper groups differ from each other by 55-60% and yet members of both groups (e.g., Spr1 and Spr2) are integrated into the DNA of one species--S. purpuratus. Below the lower underline is listed the only known representative of a very distant group, which occurs in starfish DNA. In spite of large divergence, amino acid sequence comparisons indicate that all of the elements shown in the array are members of the LTR-containing class of retrotransposons that includes Gypsy of Drosophila and Ty3 of yeast. Of all known mobile elements this class shows the closest sequence similarity to retroviruses and has the same arrangement of genes as simpler retroviruses.
在海洋物种中已鉴定出8个新的吉普赛/ Ty3类反转录转座子实例。使用来自高度保守区域的简并引物扩增了一个525个核苷酸的pol基因编码区，这将吉普赛/ Ty3的识别范围扩展到了远超过先前已知的范围。以下矩阵显示了pol基因编码区这一片段翻译后的氨基酸差异百分比。[表格：见原文]下划线将三类反转录转座子区分开来，可根据此氨基酸序列进行识别。新的上组显示，鲱鱼、海胆、海星和被囊动物DNA中的成员之间具有惊人的氨基酸序列相似性。例如，鲱鱼元件与玻璃海鞘元件的差异仅为41%，与海胆元件的差异为46%。线之间的组包括与先前已知元件（用星号标记）相近的成员，目前仅在海胆中发现。两个上组彼此之间的差异为55 - 60%，但两组的成员（例如Spr1和Spr2）都整合到了一个物种——紫球海胆的DNA中。在下划线下方列出的是一个非常远的组中唯一已知的代表，它存在于海星DNA中。尽管差异很大，但氨基酸序列比较表明，阵列中显示的所有元件都是含长末端重复序列（LTR）的反转录转座子类的成员，该类包括果蝇的吉普赛元件和酵母的Ty3元件。在所有已知的可移动元件中，这类元件与逆转录病毒显示出最接近的序列相似性，并且与更简单的逆转录病毒具有相同的基因排列。
