title: The deletion of an extra six nucleotides in the 5' -untranslated region of the nucleoprotein gene of Newcastle disease virus NA-1 decreases virulence.
abstract: BACKGROUND
  The virulent Newcastle disease virus (NDV) strain NA-1 (genotype VII) was isolated from an epizootic involving a flock of geese in Jilin Province, Northeast China, in 1999. Compared with the classical NDV strains, which have a genome size of 15,186 bp, the more recently isolated NDV strains, including that involved in the goose outbreak, have an extra six nucleotides in the 5'-untranslated region (UTR) of the nucleoprotein (NP) gene. This extra sequence, TCCCAC, is highly conserved and has been found in multiple NDV strains, including ZJ-1, WF00G, JSG0210, and NA-1. In the current study, an infectious clone from strain NA-1 was isolated and designated rNA-1. Subsequently, strain rNA-1 was mutated to delete the six-nucleotide insertion, producing strain rNA-1(-). Virulence of the recombinant virus was then assayed in chickens and geese.
  
  
  RESULTS
  The recombinant virus rNA-1(-) showed similar biological characteristics to the parental NA-1 strain in DF-1 chicken fibroblast cells. However, the virulence of rNA-1(-) in 9-day-old embryonated chicken eggs and 1-day-old specific pathogen-free (SPF) chickens was decreased compared with the rNA-1 control. Furthermore, the virulence of the recombinant strain was slightly decreased in 1-day-old SPF chickens when compared with that in 1-day-old geese.
  
  
  CONCLUSIONS
  Following deletion of six nucleotides in the 5'-UTR of the NP gene of NDV strain NA-1, the virulence of the rNA-1(-) recombinant strain was decreased in both chickens and geese. However, rNA-1(-) was more virulent in chickens than geese, as seen by the higher intracerebral pathogenicity index value.
authors.affiliation: Laboratory of Infectious Diseases, College of Veterinary Medicine, Jilin University, Changchun, 130062, China. jiaxuliu99@hotmai.com.
authors.forename: Jiaxu
authors.initials: J
authors.lastname: Liu
authors.affiliation: Laboratory of Infectious Diseases, College of Veterinary Medicine, Jilin University, Changchun, 130062, China. congyanlong@126.com.
authors.forename: Yanlong
authors.initials: Y
authors.lastname: Cong
authors.affiliation: Laboratory of Infectious Diseases, College of Veterinary Medicine, Jilin University, Changchun, 130062, China. yin@jlu.edu.cn.
authors.forename: Renfu
authors.initials: R
authors.lastname: Yin
authors.affiliation: Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, 200241, China. shoveldeen@shvri.ac.cn.
authors.forename: Chan
authors.initials: C
authors.lastname: Ding
authors.affiliation: Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, 200241, China. yus@shvri.ac.cn.
authors.forename: Shengqing
authors.initials: S
authors.lastname: Yu
authors.affiliation: Animal Infectious Disease Laboratory, College of Veterinary Medicine, Yangzhou University, Yangzhou, Jiangsu, 225009, China. xfliu@yzu.edu.cn.
authors.forename: Xiufan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Engineering Research Center of Jilin Province for Animals Probiotics, College of Animal Science and Technology, Jilin Agricultural University, Changchun, 130118, China. wangchunfeng@jlau.edu.cn.|Engineering Research Center of Chinese Ministry of Education for Edible and Medicinal Fungi, Jilin Agricultural University, Changchun, 130118, China. wangchunfeng@jlau.edu.cn.
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Wang
authors.affiliation: Laboratory of Infectious Diseases, College of Veterinary Medicine, Jilin University, Changchun, 130062, China. dingzhuangjlu@126.com.
authors.forename: Zhuang
authors.initials: Z
authors.lastname: Ding
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D000818:Animals; D015153:Blotting, Western / Q000662:veterinary; D002645:Chickens / Q000821:virology; D003001:Cloning, Molecular; D005777:Geese / Q000821:virology; D017353:Gene Deletion; D009521:Newcastle Disease / Q000821:virology; D009522:Newcastle disease virus / Q000235:genetics* / Q000472:pathogenicity; D009698:Nucleoproteins / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D014774:Virulence / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D009698:Nucleoproteins