Unnatural amino acid orthogonal translation machinery can insert unnatural amino acids at desired sites of protein through stop codon by means of foreign orthogonal translation system composed of aminoacyl-tRNA synthetase and orthogonal tRNA genes. This new genetic engineering technology is not only a new tool for biochemical researches of proteins, but also an epoch-making technology for the development of new-type live viral vaccines. The mutated virus containing premature termination codon in genes necessary for replication can be propagated in transgenic cells harboring unnatural amino acid orthogonal translation machinery in media with corresponding unnatural amino acid, but it cannot replicate in conventional host cells. This replication-deficient virus is a new-type of live viral vaccine that possesses advantages of high efficacy of traditional attenuated vaccine and high safety of killed vaccine. This article reviews the application and prospect of unnatural amino acid orthogonal translation machinery in the development of novel replication-deficient virus vaccines.
Amino Acids ; genetics ; Amino Acyl-tRNA Synthetases ; Genetic Engineering ; Protein Engineering ; RNA, Transfer ; Viral Vaccines

【Objective】 To investigate the electronic screen exposure of preschool children in Longhua District of Shenzhen, and to analyze the influencing factors. 【Methods】 A total of 25 266 children in kindergarten in Longhua District of Shenzhen were selected as study subjects. A self-designed questionnaire (completed by their guardians) was used to investigate the use of electronic products in the families of preschoolers in April 2019. 【Results】 A total of 23 407 valid questionnaires were collected in this survey, of which 12 593 (53.80%) were boys and 10 814 (46.20%) were girls; and 17 188(73.43%) children were 5 years old. Among the surveyed children, the rate of excessive exposure to electronic screens (>1h/d) was 37.72%, and 6.40% of preschool children used electronic products for more than 2 hours per day. There were statistically significant differences between the excessive exposure group and the non-excessive exposure group in gender, household registration, parents′ educational level, average monthly household income, whether exclusive electronic products,whether restriction of children′s use of electronic products, whether living with elders, only children or not, and the type of main caregiver (P<0.05). Multivariate binary Logistic regression analysis showed that girls, mothers with college education or above,not living with elders,primary caregivers being parents or nannies/others,and no exclusive electronic products were protective factors for children′s excessive exposure to electronic products(P<0.05).Non-household resident population,not-only child,and non-restriction of children′s use of electronic products were risk factors for children′s excessive exposure to electronic products(P<0.05). 【Conclusions】 The excessive use of electronic products in preschoolers is a common phenomenon in Longhua district, Shenzhen. Therefore, it is necessary to strengthen the intervention on the use time of electronic products in preschoolers, and pay more attention to the influence of family environmental factors.