EXPRESSION OF NUCLEOCAPSID VIRAL PROTEINS IN THE BACTERIAL SYSTEM OF Escherichia coli: THE INFLUENCE OF THE CODON COMPOSITION AND THE UNIFORMITY OF ITS DISTRIBUTION WITHIN GENE

A heterologous host has got a unique expression ability of each gene. Differences between the synonymous sequences play an important role in regulation of protein expression in organisms from Escherichia coli to human, and many details of this process remain unclear. The work was aimed to study the composition of codons, its distribution over the sequence and the effect of rare codons on the expression of viral nucleocapsid proteins and their fragments in the heterologous system of E.coli. The plasmid vector pJC 40 and the BL 21 (DE 3) E. coli strain were used for protein expression. The codon composition analysis was performed using the online resource (www.biologicscorp.com). 10 recombinant polypeptides were obtained encoding the complete nucleotide sequence of nucleocapsid proteins (West Nile and hepatitis C viruses) and the fragments including antigenic determinants (Lassa virus, Marburg, Ebola, Crimean-Congo hemorrhagic fever (CCHF), Puumaravala, Hantaan, and lymphocytic choriomeningitis (LHM)). Hybrid plasmid DNAs provide efficient production of these proteins in the prokaryotic system with the recombinant protein yield varying by a factor of 8: from 5 to 40 mg per 1 liter of bacterial culture. No correlation was found between the level of protein expression and the frequency of occurrence of rare codons in the cloned sequence: the maximum frequency of occurrence of rare codons per cloned sequence was observed for the West Nile virus (14.6%), the minimum was for the CCHF virus (6.6%), whereas the expression level for these proteins was 30 and 5 mg/L culture, respectively. The codon adaptation index (CAI) values, calculated on the basis of the codon composition in E. coli, for the cloned viral sequences were in the range from 0.50 to 0.58, which corresponded to the average expressed proteins. The analysis of the distribution profiles of CAI in the cloned sequences indicated the absence of clusters of rare codons that could create difficulties in translation. A statistically significant difference between the frequencies of the distribution of amino acids in the cloned sequences and their content in E. coli was observed for the nucleocapsid proteins of the Marburg, Ebola, West Nile, and hepatitis C viruses.