摘 要 ：在原核生物和植物叶绿体中，RPS4（ribosomal protein small subunit 4）在核糖体30S小亚基形成起始过程中发挥重要作用；该蛋白在植物中由叶绿体rps4基因编码。为验证蕨类植物在白垩纪适应被子植物兴起而发生分化的观点，本文以23种蕨类植物为研究对象，利用分支模型、位点模型和分支位点模型对其叶绿体rps4基因进化适应性进行分析。分支模型检测到4个可能存在正选择的分支；位点模型和分支位点模型虽然没有检测出正选择位点，但是位点模型检测出了85个负选择位点。通过研究我们仅仅得出a、b两个代表水龙骨类的分支处于正选择压力下，这与水龙骨类在白垩纪发生辐射式演化的理论相一致。同时rps4基因处于强烈的负选择压力这一事实表明该基因的功能与结构已经趋于稳定。
Abstract:RPS4 (ribosomal protein small subunit 4) is one of the primary rRNA-binding proteins that initiate assembly of the 30S subunit in prokaryotes and plant chloroplast. In ferns, RPS4 is encoded by chloroplast gene rps4. Recently polypod ferns have been demonstrated to undergo diversification in the Cretaceous after the rise of angiosperms. To further test this proposal, an adaptive evolutionary analysis was performed on the rps4 gene sequences of 23 types of ferns, under the branch model, site model and branch-site model developed by Yang et al. The results from branch model indicated that 4 lineages were under the positive selection with ω>1. No positive selected sites were detected under the branch-site model, however, 85 negative selected sites were identified under the site model. There were only 2 lineages from Polypodiaceous ferns which are under positive selection. And this finding was constant with the proposal we had mentioned before. Moreover, the fact that rps4 was under highly negative selection indicated that the function and structure of rps4 had been almost stabilized.