Genetic variation in porcine reproductive and respiratory syndrome virus isolates in the midwestern United States
Genetic variation in porcine reproductive and respiratory syndrome virus isolates in the midwestern United States
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DOI：
10.1099/0022-1317-77-6-1271
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发表时间：
1996-06-01
影响因子：
3.8
通讯作者：
Murtaugh, MP
中科院分区：
文献类型：
--
作者：
Kapur, V;Elam, MR;Murtaugh, MP
对从美国中西部地区回收的10株猪繁殖与呼吸综合征病毒(PRRSV)开放阅读框(ORF)2至7的3266个碱基区的核苷酸序列进行了测定。两两比较表明，分离株之间的遗传距离在2.5%到7.9%之间(平均为5.8%+/-0.2%)，而来自欧洲的Lelystad株与美国克隆株的平均遗传距离为34.8%。因此，美国和欧洲的PRRSV分离株代表着同一病毒在基因上的不同集群。编码包膜糖蛋白的ORF5多态程度最高[总核苷酸多样性(Pi)=0.097+/-0.007]，编码病毒M蛋白的ORF6最保守(pi=0.038+/-0.003)。ORF之间核苷酸多样性的显著差异表明，病毒是通过简单积累随机中性突变以外的过程进化的。为了支持这一假设，对核苷酸序列的统计分析为ORF2、3、4、5和7中的基因内重组或基因转换提供了强有力的证据，但在ORF6中没有。在所有6个ORF中都观察到了过量的同义(沉默)替换，表明存在着保存氨基酸序列的进化压力。综上所述，这些数据表明，尽管现有的PRRSV分离株之间进行了基因内重组，但纯化选择保持了单个ORF的一级结构。
The nucleotide sequence of a 3266 bp region encompassing open reading frames (ORFs) 2 through 7 of the porcine reproductive and respiratory syndrome virus (PRRSV) was determined for 10 isolates recovered from the midwestern United States. Pairwise comparisons showed that genetic distances between isolates ranged from 2.5% to 7.9% (mean 5.8% +/- 0.2%) whereas the Lelystad strain from Europe was, on average, 34.8% divergent from US clones. Thus, US and European PRRSV isolates represent genetically distinct clusters of the same virus. ORF 5, which encodes the envelope glycoprotein, was the most polymorphic [total nucleotide diversity (pi) = 0.097 +/- 0.007] and ORF 6, encoding the viral M protein, was the most conserved (pi = 0.038 +/- 0.003). The substantial differences in nucleotide diversity among ORFs suggests that the virus is evolving by processes other than simple accumulation of random neutral mutations. In support of this hypothesis, statistical analyses of the nucleotide sequence provided strong evidence for intragenic recombination or gene conversion in ORFs 2, 3, 4, 5 and 7, but not in ORF 6. An excess of synonymous (silent) substitutions was observed in all six ORFs, indicating an evolutionary pressure to conserve amino acid sequences. Taken together, the data indicate that despite intragenic recombination among extant PRRSV isolates, purifying selection has acted to maintain the primary structure of individual ORFs.