球形棕囊藻(Phaeocystis globosa)叶绿体psaA基因片段的序列分析

根据GenBank中检索到的南极棕囊藻(Phaeocystis globosa)psaA基因序列设计psaAL和psaAR引物，对球形棕囊藻(Phaeocystis globosa)，的psaA基因片段进行PCR扩增并测序，获得了629bp的DNA序列。应用clustal X对球形棕囊藻P1、P2株系和南极棕囊藻的psaA基因片段序列进行比对，结果表明，球形棕囊藻psaA基因片段序列无插入／缺失，核苷酸差异率为3.34％。应用DNAstar分析软件推断球形棕囊藻和南极棕囊藻的psaA基因对应的氨基酸序列和RNA二级结构，发现它们的氨基酸序列差异不大，序列中209个氨基酸只有1个发生了变化，其氨基酸变异率为0．48％；除部分结构域比较相似外，RNA二级结构上体现一定程度的差异，这可能对棕囊藻的分子分类研究有参考价值。因所获得的psaA基因片段序列及氨基酸序列具有种的极端保守性，不适宜用作Phaeocystis属种间的分子分类研究。

Sequence Analyses of Chloroplastic psaA Gene Fragment from Phaeocystis globosa

Based on the complete psaA gene sequence of Phaeocystis antarctica in GenBank, two primers psaAL and psaAR were designed to amplify psaA gene sequence fragment of Phaeocystis globosa. An unambiguous sequence of 629 bp was gained,which was aligned with the complete psaA gene of Phaeocystis antarctica in Clustal X. The corresponding nucleotide dissimilarity of the two sequences was only 3.34%, and no insertion/ deletion was found. The relative amino acid sequence and RNA secondary structure were concluded in DNAstar. The concluded amino acid sequence was also conservative, and there was only one distinct base among 209 amino acids, with the difference of 0.48%. However, the concluded RNA secondary structures were quite unlike, apart from a few conservative domains. Perhaps the secondary structure of RNA may benefit the study on taxonomy of Phaeocysitis. It is considered that the DNA sequences and amino acid sequences of psaA are conservative, which is unadvisable to use for molecular interspecific classification of the genus Phaeocysitis.