Effect of genetic variations of influenza virus nucleoprotein on virus replication

• Main Authors: Su-JhenHung, 洪素珍
• Other Authors: Jen-Ren Wang
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/ge5vv4

碩士 === 國立成功大學 === 醫學檢驗生物技術學系 === 102 === Influenza A virus causes severe pandemics and annual epidemics through its RNA genome segment reassortment and frequent gene mutations. The RNA together with viral polymerase PB2, PB1, PA and nucleoprotein (NP) form the ribonucleoprotein (RNP) complexes, which are the functional units for viral genome transcription and replication. In RNP, NP plays an important role on polymerase activity by interaction with viral polymerase, vRNA and multiple host factors. Here, we aim to investigate the NP genetic evolution in human and characterize the effect of identified variations. NP genes of randomly selected H3N2 clinical isolates from 1999 to 2014 were sequenced and many genetic variations were identified. Phylogenetic analysis showed NP genes can be divided into 6 clades. Five NP genes from different clades were cloned into plasmid for the mini-genome assay to analyze the effect of NP genetic variations. The results showed that NP of Taiwan/N1215/07 virus had significantly higher polymerase activity than NP from other isolates; in contrast, NP of Taiwan/N3446/02 had significantly lower polymerase activity both at 33℃ and 37℃. By site-directed mutagenesis, we found that S450G of NP gene increased the polymerase activity but K31R decreased the activity. Furthermore, alanine substitutes of 31 and 450 residues significantly decreased the polymerase activity and virus growth in vitro. In conclusions, by analyzing the genetic variations identified from clinical isolates, we demonstrated that residues 31 and 450 of NP contribute to viral polymerase activity as well as virus replication, indicating the evolutionary genetic variations of NP play roles on functional change of influenza virus.