病毒基因組在不斷地遭受突變,，但是有害的突變往往能夠被逆轉(zhuǎn)或者因?yàn)樵俅瓮蛔兌謴?fù)正常,。HIV-1 作為逆轉(zhuǎn)錄病毒,，其不精確性復(fù)制往往會(huì)造成大量不同的病毒基因序列。到目前為止,，對(duì)于病毒蛋白比如Tat（一種在病毒基因表達(dá)以及復(fù)制中起決定作用的蛋白）是如何維持其復(fù)雜功能的機(jī)制還不清楚,。
盡管HIV-1的Tat基因有著相當(dāng)多的序列多樣性,，它如何執(zhí)行復(fù)雜功能的機(jī)制還沒(méi)有被完全了解。近日,，美國(guó)加州大學(xué)聯(lián)合我國(guó)廈門大學(xué)制藥科學(xué)學(xué)院發(fā)現(xiàn)一項(xiàng)重要成果：即Tat中兩個(gè)特殊位點(diǎn)對(duì)調(diào)節(jié)病毒兩種截然不同的基因表達(dá)機(jī)制具有決定作用,，并且，這對(duì)維持Tat功能以及影響病毒的潛伏性可能具有重要作用,。
Tat蛋白中有幾種重要的保守氨基酸位點(diǎn),，這此次實(shí)驗(yàn)中，研究人員假設(shè)這些位點(diǎn)中含有重要的功能性的殘基,，并且假設(shè)它們不是彼次孤立的保守而是作為關(guān)聯(lián)對(duì)出現(xiàn),。為了確定這樣的位點(diǎn)，他們使用交互信息分析和生化實(shí)驗(yàn)來(lái)鑒定這樣的協(xié)同進(jìn)化的位點(diǎn),，結(jié)果發(fā)現(xiàn),，殘基35以及39是高度關(guān)聯(lián)的。并且,，在大量隔離的缺陷病毒中,，往往會(huì)出現(xiàn)這對(duì)殘基的突變。然而,，當(dāng)對(duì)異種的Tat序列引入這兩種突變時(shí),，其基因表達(dá)會(huì)表現(xiàn)得接近于野生型。此外,，對(duì)比于大多數(shù)因?yàn)閰f(xié)同進(jìn)化而具有相似功能的蛋白殘基,，結(jié)構(gòu)模型和生化研究表明，這兩種殘基造成了兩種完全不同的基因表達(dá)步驟：偶聯(lián)P-TEFb或者促進(jìn)RNAPII的C末端結(jié)構(gòu)域P-TEFb的蛋白磷酸化,。而且,，在模仿B型或者C型的HIV-1的Tat變異體中，其35和39位點(diǎn)都出現(xiàn)了進(jìn)化優(yōu)勢(shì),，即P-TEFb偶聯(lián)病毒RNAPII的磷酸化,，這表明HIV-1的亞型已經(jīng)進(jìn)化出可以獲得相同基因表達(dá)水平的轉(zhuǎn)錄策略。（生物谷Bioon.com）
doi: 10.1074/jbc.M111.302653
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Mutual Information Analysis Reveals Coevolving Residues in Tat That Compensate for Two Distinct Functions in HIV-1 Gene
Siddharth S. Dey, Yuhua Xue, Marcin P. Joachimiak, Gregory D. Friedland, John C. Burnett, Qiang Zhou, Adam P. Arkin and David V. Schaffer.
Viral genomes are continually subjected to mutations, and functionally deleterious ones can be rescued by reversion or additional mutations that restore fitness. The error prone nature of HIV-1 replication has resulted in highly diverse viral sequences, and it is not clear how viral proteins such as Tat, which plays a critical role in viral gene expression and replication, retain their complex functions. Although several important amino acid positions in Tat are conserved, we hypothesized that it may also harbor functionally important residues that may not be individually conserved yet appear as correlated pairs, whose analysis could yield new mechanistic insights into Tat function and evolution. To identify such sites, we combined mutual information analysis and experimentation to identify coevolving positions and found that residues 35 and 39 are strongly correlated. Mutation of either residue of this pair into amino acids that appear in numerous viral isolates yields a defective virus; however, simultaneous introduction of both mutations into the heterologous Tat sequence restores gene expression close to wild-type Tat. Furthermore, in contrast to most coevolving protein residues that contribute to the same function, structural modeling and biochemical studies showed that these two residues contribute to two mechanistically distinct steps in gene expression: binding P-TEFb and promoting P-TEFb phosphorylation of the C-terminal domain in RNAPII. Moreover, Tat variants that mimic HIV-1 subtypes B or C at sites 35 and 39 have evolved orthogonal strengths of P-TEFb binding versus RNAPII phosphorylation, suggesting that subtypes have evolved alternate transcriptional strategies to achieve similar gene expression levels..
