Chemical synthesis and expression in E. coli of a human Val8-calcitonin gene by fusion to a synthetic human interferon-gamma gene

Efficiency of a novel non-Shine-Dalgarno and a Shine-Dalgarno consensus sequence to initiate translation in Escherichia coli of genes with different downstream box composition

The efficiency of a novel non-Shine-Dalgarno translational initiator (ACCUACUCGAGUUAG, denoted PL) to promote translation in Escherichia coli was compared with that of the Shine-Dalgarno (SD) consensus sequence (AAGGAGGU) using four reporter genes. The obtained results showed that the genes of pokeweed antiviral protein (PAP I) and human calcitonin (CT) were poorly expressed under the conventional SD and were better expressed under the PL sequence. On the contrary, the genes of human interferon gamma (hIFN gamma) and chloramphenicol acetyltransferase (CAT) were highly expressed under SD and poorly expressed under the PL sequence. Computer search revealed a great diversity between the four reporter genes in respect to their complementarity to E. coli 16S rRNA. PAP I and CT genes were rich in nucleotides matching 16S rRNA (called downstream boxes) whereas the complementary domains in the other two (hIFN-gamma and CAT) genes were much shorter. The different behavior of the four reporter genes when placed under the translational control of SD and PL sequences was explained by the different binding energy of their mRNAs to the 30S ribosomal subunit.

Gene expression evidence indicates that nucleotides 507-513 and 1434-1440 in 16S rRNA are organized in close proximity on the Escherichia coli 30S ribosomal subunit

A non-Shine-Dalgamo translational initiator is identified in Escherichia coli. The nucleotide sequence ACCUACUCGAGUUAG, designated as PL, is capable of initiating translation of pokeweed antiviral protein (PAP) and human calcitonin (hCT) mRNAs in E. coli cells. The yield of recombinant protein was double that obtained with the consensus Shine-Dalgarno-sequence-(SD)-driven translation. The PL sequence is composed of two heptanucleotides (ACCUACU, box I and GAGUUAG, box II) which are complementary to nucleotides 1434-1440 and 507-513, respectively, in 16S rRNA. Mutational analysis shows that the translation initiation efficiency with either box alone is much lower than that obtained with the entire PL sequence, indicating that the boxes interact simultaneously with both complementary regions in 16S rRNA during the translation initiation step. Based on these results, we propose that the two widely separated regions 507-513 (part of helical domain 18) and 1434-1440 (belonging to helical domain 44) are organized in close proximity to each other and to the ribosome decoding center on the surface of the E. coli 30S ribosomal subunit.

Comparative study on the effect of signal peptide codons and arginine codons on the expression of human interferon-alpha 1 gene in Escherichia coli

Human interferon-alpha 1 (HuIFN-alpha 1) gene containing signal peptide codons is poorly expressed in bacteria, and this is explained by the presence of clusters of rare (AGG) arginine codons in its structure. In this study, we have constructed a series of modified HuIFN-alpha 1 genes to study the effect of both residual signal peptide codons and clusters of AGG codons on gene expression in Escherichia coli cells. Our results showed that substitution of preferential for rare arginine codons in two clusters did not affect the yield, whereas deletion of the signal peptide codons led to a 10-fold increase in the yield of recombinant protein. To understand the mechanism of interference of gene structure on the expression of the HuIFN-alpha 1 gene in vivo, both the level and stability of HuIFN-alpha 1 mRNA were measured. The amount of HuIFN mRNA increased almost five times on deletion of the signal peptide codons from HuIFN-alpha 1 gene constructs (containing AGG clusters or not). The stability of mRNA obtained from all gene constructs was shown to be the same (half-life of 60 +/- 5 secs), indicating that the signal peptide codons interfere with both the efficiency of transcription of the HuIFN-alpha 1 gene and translation of its mRNA.

Efficiency of the 5'-terminal sequence (omega) of tobacco mosaic virus RNA for the initiation of eukaryotic gene translation in Escherichia coli

Recent studies have demonstrated that the 5' leader (omega sequence) of tobacco mosaic virus RNA has a certain enhancing capacity for translation of mRNA in both prokaryotes and eukaryotes. In order to estimate the efficiency of omega to initiate translation of mRNA in Escherichia coli, in comparison to the Shine-Dalgarno (S/D) sequence, we have inserted eight different eukaryotic genes into two types of E. coli expression vectors containing one constitutive promoter (P1) but different translation-initiation sites (S/D or omega delta 3 sequence, respectively). The efficiency of transcription and translation in vivo was evaluated for these vectors by measuring the yield of protein and both the level and stability of mRNA. We report that substitution of omega delta 3 for S/D decreases the yield of expressed protein 4-1900-fold and the content of gene-specific mRNA is decreased by about sevenfold. However, in comparison with the S/D sequence, the level of protein expressed under the translational control of omega delta 3 is less sensitive to changes in the 5' coding region. We also report that the omega sequence contains a region of 10-12 nucleotides complementary to the small ribosomal subunit RNA (rRNA) of E. coli, Eikenella corrodens and Xenopus laevis, and to the rRNA of the (small ribosomal) subunit of Oryza sativa.

Two methods for rapid assembly and oligomerization of synthetic genes: construction of human calcitonin-encoding sequences

Two fast, simple and reliable methods for construction of synthetic genes are described. The first represents a one-vial method for assembly and cloning of monomeric genes, and the second allows a simultaneous assembly, oligomerization and cloning of synthetic genes. Both methods consist of ligation of the synthetic oligodeoxyribonucleotides (oligos) building up the gene directly into the cloning vector, followed by screening of the recombinant clones for the presence of specific gene constructs. The average length of the oligomeric genes thus constructed is directly proportional to the molar ratio between the vector DNA and the synthetic oligos used. Both methods are illustrated by the construction of a series of human calcitonin-encoding genes.

Shotgun concatenation of synthetic genes: construction of concatemeric human calcitonin genes

A new fast and reliable approach for construction of concatemeric synthetic genes is described. The method consists of shotgun polymerization of three truncated monomeric gene units using a specific linker, followed by cloning of the recombinant clones and screening them for the presence of concatemeric genes of defined length. The method is illustrated by constructing a series of tandemly repeated human calcitonin (hCT) genes.

Construction of a Co1E1 plasmid bearing inducible high-copy-number phenotype

In order to construct plasmids bearing inducible high-copy-number phenotype, the cloning plasmid pBR322 was modified as follows: a DNA fragment containing a strong synthetic promoter (P1), synthetic lac operator (O1), DNA sequence corresponding to the RNAI/RNAII region of the Co1E1 replicon and the CAT gene transcription terminator was substituted for the 29 bp EcoRI/HindIII DNA fragment. Two types of plasmids were constructed in this way, differing in the orientation of the RNAI/RNAII fragment. Depending on the orientation these plasmids coded for RNA molecules representing either RNAI or RNAII domains. It was found that when RNAII molecules were overproduced the plasmid copy number was about 4 times higher than that of pBR322 and only negligible change in the plasmid copy-number value was observed upon overproduction of RNAI molecules.

Expression of synthetic calcitonin genes in plasmid vectors containing tandemly repeated non-overlapping ribosome binding sites

1. Expression plasmids containing non-overlapping tandemly repeated ribosome binding sites (RBS) were constructed in order to stabilize mRNA and enhance translation. 2. Two synthetic genes (human calcitonin tetramer gene and a fusion gene human gamma-interferon-human calcitonin) were cloned in these vectors and the effect of multiplicity of Shine-Dalgarno (S/D) sequence on heterologous gene expression was studied. 3. It was found that duplication and triplication of RBS had no effect on the stability of mRNA but led to a strong decrease in the level of recombinant protein and mRNA in the cell. 4. Plasmids bearing four times repeated S/D sequences gave longer-lived mRNAs and maintained a level of protein and mRNA very close to the values obtained with a single S/D containing plasmids.

Constitutive expression of a native human interferon-alpha 1 gene in Escherichia coli

1. A plasmid for constitutive expression of the human interferon-alpha 1 (hIFN-alpha 1) gene in Escherichia coli is constructed on the basis of the cloning plasmid pBR322 using a strong synthetic promoter, synthetic ribosome binding site and a native hIFN-alpha 1 gene excised from a chromosomal clone. 2. The yield of recombinant hIFN-alpha 1 from E. coli LE392 cells transformed with the expression plasmid pJP1R9-hIFN-alpha 1 is evaluated to be 2-6 x 10(7) U/l bacterial culture for metabolic shaker and 6-8 x 10(7) U/l for fermentor.

Determination of plasmid copy number by the "boiling" method

A fast and reliable approach for determination of plasmid copy number in Escherichia coli is proposed, based on the "boiling" method (5) for separation of plasmid and chromosomal DNA. The method includes in vivo uniform labeling of total bacterial DNA, separation of DNA into plasmid and chromosomal DNA fractions, and quantitation of DNA in the two fractions by radioactivity measurement. No isolation and purification of native DNA are necessary.