水溞基因组P450基因家族的分析

A GENOME-WIDE ANALYSIS OF P450 GENE FAMILY IN WATERFLEA(Daphnia pulex)

利用水溞基因组mRNA和氨基酸数据库对P450基因进行搜索和分析,结果显示:在水溞基因组中发现71个P450基因,它们分别属于15个P450家族和17个亚家族,是一个典型的多基因家族。以氨基酸相似度大于60%为标准对水溞P450基因进行分组,则71个P450基因中,16个为孤儿基因,不能被归入任何一组;其余55个可归入12个组,其中8个组,包含47条序列适合于正选择和基因转换分析。结果表明:有3个组,含22个基因显著受到正选择压力作用,其中的2个组,含18个基因有正选择概率大于95%的氨基酸位点228E或277T,228E和277T分别位于底物识别位点SRS2和SRS5;有5个组,包含19个基因显示显著的基因转换事件;既显著受到正选择压力作用,又参与基因转换的基因共12个;相反,检测出既没有受到显著的正选择压力作用,又没有基因转换的基因18个。可见,发生基因转换的基因与受到显著正选择的基因有高度的相关性:发生过基因转换的基因中63.2%都受到显著的正选择压力作用,同时,受正选择压力作用的基因中有54.5%发生了基因转换。此外,鉴定出20个不同的基序,其中有5条基序在90%以上的基因中出现。

A genome-wide analysis of P450 genes was performed in waterflea genome based on their mRNA and amino acid data. Seventy-one P450 genes, assigned into 15 gene families and 17 subfamilies, were identified. They were partitioned into 12 groups and 16 orphan genes by a criterion that the genes belong to the same group when their amino acid identity was more than 60%. Except orphan genes and 4 gene groups, including 2 genes per group, positive selection and gene conversion were analyzed in other 8 groups, including 47 genes. The results showed that positive selection was detected in 3 groups （including 22 genes）. The positively selected sites 228E or 277T, locating in SRS （substrate recognition sites） 2 or SRS 5, were detected in 2 groups （18 sequences） with a more than 95% probability, and gene conversions were detected in 5 groups （19 sequences）. Interestingly, both positive selection and gene conversion events were identified obviously in 12 genes, and neither positive selection nor gene conversion event was detected in 18 genes. The correlation was revealed between positive selection and gene conversion： positive selection sites were identified in 63.2% of genes in which gene conversion events were detected, and gene conversion events were identified in 54.5% of genes in which positive selections were detected. Moreover, twenty motifs were identified, thereinto, 5 motifs existed in over 90% of P450 genes.