Effects of poly(A) tails with different lengths on mRNA expression in vitro and stability of transcription template in Escherichia coli / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To investigate the effects of poly(A) tails with different lengths on mRNA expression in vitro and the passage stability of transcription template with poly (A) tail in Escherichia coli ( E. coli). Methods:Plasmids with poly(A) tails of 38, 60, 103, 125 and 126 (60 nt+ 6 nt spacer+ 60 nt) nt were designed and constructed. Then the plasmids were linearized by single enzyme digestion and used as transcription template for preparing enhanced green fluorescent protein (EGFP)-mRNA. EGFP-mRNA containing poly(A) tails of different lengths were transfected into 293T cells and the expression of EGFP was detected by flow cytometry. As to stability test, the template plasmids with poly (A) tail of 125 and 126 nt were transformed into E. coli TransStbl3 and Top10 competent cells. Seven clones were selected for culture and plasmid extraction, and then the plasmids were digested by restriction enzyme and detected by capillary electrophoresis. For passage stability, three correctly sequenced clones of each group were selected for continuous passage at 37℃, and the plasmids were extracted and digested every two generations for capillary electrophoresis. At the same time, the correctly sequenced clones of 125 nt group were also passaged at 30℃, and the plasmids were also extracted and digested every two generations for capillary electrophoresis. Results:The transcription templates with poly(A) tail of different lengths were successfully constructed. Flow cytometry showed that the fluorescence expression of the template plasmids with poly (A) tail of 103 and 125 nt were significantly higher than that of 38 and 60 nt. The fluorescence expression of the plasmid with poly (A) tail of 126 nt was significantly higher than that of all other groups. The percentages of stable sequences of the template plasmid with poly(A) tail of 125 nt in TransStbl3 and Top10 competent cells were 76% and 91%, respectively. The results of continuous passage showed that poly(A) tail of 125 nt could be stable to the 4th generation at 37℃ in both TransStbl3 and Top10 competent cells, and stable to the 16th and 10th generations at 30℃. The percentages of stable sequences of the template plasmid with poly(A) tail of 126 nt in TransStbl3 and Top10 competent cells were 95% and 48%, respectively. The results of continuous passage showed that poly(A) tail of 126 nt could be stable to the 12th generation at 37℃ in both TransStbl3 and Top10 competent cells.Conclusions:The length and composition of poly(A) tail in mRNA affected the expression of target protein. Adding a spacer with a length of 6 nt to poly(A) tail and low temperature culture were both helpful to improve the stability of the template plasmid, which provided a reference for the design and preparation of in vitro transcription template of mRNA vaccine.