Hepatitis E Virus (HEV) Infection Among Immunocompromised Individuals: A Brief Narrative Review

Hepatitis E virus (HEV) is a single-stranded positive-sense RNA virus that belongs to Hepeviridae family. HEV is the most common cause of acute viral hepatitis worldwide. According to the World Health Organization (WHO), there are estimated 20 million HEV infections worldwide every year, leading to estimated 3.3 million symptomatic cases of HEV infection. The WHO estimates that HEV infection caused approximately 44,000 deaths in 2015, which represents 3.3% of mortality rates due to viral hepatitis. In low-income (LI) countries and lower-middle-income (LMI) countries, HEV is a waterborne infection induced by HEV genotype (gt) 1 and HEV gt 2 that cause large outbreaks and affect young individuals with a high mortality rate in pregnant women from South Asian countries and patients with liver diseases. HEV gt 3, HEV gt 4, and HEV gt 7 are responsible for sporadic infections with zoonotic transmission mainly through the consumption of raw or undercooked meat from different animals. Acute HEV infection is relatively asymptomatic or mild clinical form, in rare cases the disease can be moderate/severe clinical forms and result in fulminant hepatitis or acute liver failure (ALF). Furthermore, HEV infection is associated with extrahepatic manifestations, including renal and neurological clinical signs and symptoms. Pregnant women, infants, older people, immunocompromised individuals, patients with comorbidities, and workers who come into close contact with HEV-infected animals are recognized as major risk groups for severe clinical form of HEV infection and fatal outcome. Chronic HEV infection can occur in immunocompromised individuals with the possibility of progression to cirrhosis.

Effectiveness and safety of COVID-19 vaccines in patients with oncological diseases: State-of-the-art

Although the coronavirus disease 2019 (COVID-19) pandemic was declared to be no longer “a public health emergency of international concern” with its wide range of clinical manifestations and late complications, severe acute respiratory syndrome coronavirus 2 infection proved to be a serious threat, especially to the elderly and patients with comorbidities. Patients with oncologic diseases are vulnerable to severe infection and death. Indeed, patients with oncohematological diseases have a higher risk of severe COVID-19 and impaired post-vaccination immunity. Unfortunately, cancer patients are usually excluded from vaccine trials and investigations of post-vaccinal immune responses and the effectiveness of the vaccines. We aimed to elucidate to what extent patients with cancer are at increased risk of developing severe COVID-19 and what is their overall case fatality rate. We also present the current concept and evidence on the effectiveness and safety of COVID-19 vaccines, including boosters, in oncology patients. In conclusion, despite the considerably higher mortality in the cancer patient group than the general population, countries with high vaccination rates have demonstrated trends toward improved survival of cancer patients early and late in the pandemic.

Homo- and heterometallic complexes of Zn(II), {Zn(II)Au(I)}, and {Zn(II)Ag(I)} with pentadentate Schiff base ligands as promising anticancer agents

Two families of homo- and heterometallic complexes, [Zn2L1(μ-OH)(H2O)2](ClO4)2, [Zn2L2(μ-OH)(H2O)2](ClO4)2, [Zn2L3(μ-OH)(H2O)2](ClO4)2, 1∞[{L1Zn2(μ-OH)}{μ-[Ag(CN)2]}](ClO4), [{L1Zn2(μ-OH)}2{μ-[Au(CN)2]}{[Au(CN)2]2}](ClO4)·H2O, 1∞[{L2Zn2(μ3-OH)}2(H2O){μ-[Ag(CN)2]}](ClO4)3·THF·0.5MeOH, 1∞[{L2Zn2(μ3-OH)}2(H2O){μ-[Au(CN)2]}](ClO4)3·THF·H2O, and 1∞[{L3Zn2(μ-OH)}{μ-[Ag(CN)2]}][Ag(CN)2]·H2O, respectively, have been synthesized and characterized. The Schiff bases used as ligands were obtained by condensation reactions of 2,6-diformyl-p-cresol with N,N-dimethyl-ethylenediamine (HL1), 2-aminomethyl-pyridine (HL2), and 2-aminoethyl-pyridine (HL3), respectively. The cytotoxic/cytostatic and genotoxic effects in cultured human MCF-7 (luminal type A breast cancer), MDA-MB-231 (triple negative breast cancer), HeLa (cervical carcinoma), and Lep-3 (non-tumor embryonal fibroblastoid cells) were studied. The investigations were performed by thiazolyl blue tetrazolium bromide test (MTT test), neutral red uptake cytotoxicity assay, crystal violet staining, hematoxylin and eosin staining, double staining with acridine orange and propidium iodide, AnnexinV/FITC, and Comet assay in short-term experiments (24-72 h, with monolayer cell cultures) as well as by 3D colony-forming method in long-term experiments (28 days, with 3D cancer cell colonies). The results obtained revealed that: (i) applied at a concentration range of 0.1-100 μg mL-1, the compounds investigated decrease in a time- and concentration-dependent manner the viability and/or proliferation of the treated cells; (ii) complexes of {Zn(II)Au(I)} show relatively higher cytotoxic/genotoxic activity and antitumor potential as compared to {Zn(II)Ag(I)}; (iii) some of the complexes demonstrate more pronounced cytotoxic potential than commercially available antitumor agents cisplatin, oxaliplatin, and epirubicin.

Novel Cerium(IV) Coordination Compounds of Monensin and Salinomycin

The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and salinomycinic acids (HL) with metal ions of type M⁴⁺ and the known antiproliferative potential of antibiotics has provoked our interest in exploring the coordination processes between MonH/SalH and ions of Ce⁴⁺. (1) Methods: Novel monensinate and salinomycinate cerium(IV)-based complexes were synthesized and structurally characterized by elemental analysis, a plethora of physicochemical methods, density functional theory, molecular dynamics, and biological assays. (2) Results: The formation of coordination species of a general composition [CeL₂(OH)₂] and [CeL(NO₃)₂(OH)], depending on reaction conditions, was proven both experimentally and theoretically. The metal(IV) complexes [CeL(NO₃)₂(OH)] possess promising cytotoxic activity against the human tumor uterine cervix (HeLa) cell line, being highly selective (non-tumor embryo Lep-3 vs. HeLa) compared to cisplatin, oxaliplatin, and epirubicin.

Novel Triple Stimuli Responsive Interpenetrating Poly(Carboxybetaine Methacrylate)/Poly(Sulfobetaine Methacrylate) Network

The study reports the synthesis and characterization of novel triple stimuli responsive interpenetrating polymer network (IPN) based on two polyzwitterionic networks, namely of poly(carboxybetaine methacrylate) and poly(sulfobetaine methacrylate). The zwitterionic IPN hydrogel demonstrates the ability to expand or shrink in response to changes in three "biological" external stimuli such as temperature, pH, and salt concentration. The IPN hydrogel shows good mechanical stability. In addition, other important features such as non-cytotoxicity and antibiofouling activity against three widespread bacteria as P. Aeruginosa, A. Baumanii, and K. Pneumoniae are demonstrated. The in vivo behavior of the novel zwitterionic IPN hydrogel suggests that this smart material has very good potential as a biomaterial.

Mucosal COVID-19 vaccines: Risks, benefits and control of the pandemic

Based on mucosal immunization to promote both mucosal and systemic immune responses, next-generation coronavirus disease 2019 (COVID-19) vaccines would be administered intranasally or orally. The goal of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines is to provide adequate immune protection and avoid severe disease and death. Mucosal vaccine candidates for COVID-19 including vector vaccines, recombinant subunit vaccines and live attenuated vaccines are under development. Furthermore, subunit protein vac-cines and virus-vectored vaccines have made substantial progress in preclinical and clinical settings, resulting in SARS-CoV-2 intranasal vaccines based on the previously successfully used nasal vaccines. Additional to their ability to trigger stable, protective immune responses at the sites of pathogenic infection, the development of ‘specific’ mucosal vaccines targeting coronavirus antigens could be an excellent option for preventing future pandemics. However, their efficacy and safety should be confirmed.

Perspective Chapter: Bioinformatics Study of the Evolution of SARS-CoV-2 Spike Protein

SARS-CoV-2 belongs to the family of coronaviruses, which are characterized by spikes that sit densely on the surface of the virus. The spike protein (Spro) is responsible for the attachment of the virus to the host cell via the ACE2 receptor on the surface of the host cell. The strength of the interaction between the receptor-binding domain (RBD) of the highly glycosylated spike protein of the virus and the host cell ACE2 receptor represents the key determinant of the infectivity of the virus. The SARS-CoV-2 virus has mutated since the beginning of the outbreak, and the vast majority of mutations has been detected in the spike protein or its RBD. Since specific mutations significantly affect the ability of the virus to transmit and to evade immune response, studies of these mutations are critical. We investigate GISAID data to show how viral spike protein mutations evolved during the pandemic. We further present the interactions of the viral Spro RBD with the host ACE2 receptor. We have performed a large-scale mutagenesis study of the Spro RBD-ACE2 interface by performing point mutations in silico and identifying the ambiguous interface stabilization by the most common point mutations in the viral variants of interest (beta, gamma, delta, omicron).

Strengthening CoViD-19 therapy via combinations of RAS modulators

Evidence has accumulated that the pathology of CoViD-19 is strongly related to the renin-angiotensin system (RAS). The blockage of the angiotensin converting enzyme 2 (ACE2) by the SARS-CoV-2 virus leads to downstream consequences such as increased vascular tone, extensive fibrosis and pronounced immune reactions. Different approaches to tackle the adverse viral effects by compensating the lost ACE2 function have been suggested. Here, we use an unequal-arm lever model to describe a simplified version of the biased regulation exercised by the angiotensin II and angiotensin-(1-7) hormones, which are the substrate and the product of ACE2, respectively. We reason upon the lever dynamics and its disruptions caused by the virus, and propose that a combination of RAS modulators will most efficiently compensate the imbalance due to the excess of angiotensin II and the scarcity of angiotensin-(1-7). Specifically, we focus on the possible benefits of the simultaneous application of two agents, a MAS-receptor agonist and an angiotensin-II-type-2-receptor agonist. We conjecture that this combination has the potential to introduce a beneficial synergistic action that promotes anti-hypoxic, anti-fibrotic and anti-proliferative effects, thereby improving the clinical management of acute and chronic CoViD-19 pathologies.

Spectral properties and biological activity of La(III) and Nd(III) Monensinates

The present research is focused on evaluation of complexation ability of Monensic acid (MonH) towards La3+ and Nd3+ ions.

Changes in the SRCD spectrum of Monensinate anion were monitored upon addition of lanthanide(III) ions. The antibiotic undergoes formation of one neutral ([Ln(Mon)3(H2O)3]) and two positively charged complex species of composition [Ln(Mon)2(H2O)2]+ and [Ln(Mon) (H2O)]2+, respectively (Ln = La3+, Nd3+). Neutral complexes were isolated as fine powders and were characterized by IR, FAB-MS and ESI-MS. It is assumed that Monensin acts in bidentate coordination mode via monodentate carboxylate moiety and hydroxyl group, both located at the opposite ends of antibiotic molecule.

Activity of Monensic acid and [Ln(Mon)3(H2O)3] to decrease visible bacteria growth of B. subtilis, S. Lutea and B. mycoides was evaluated by agar hole diffusion method. Results showed that complexation of lanthanide(III) ions to Monensin enhances the activity of non-coordinated ligand.

Antitumor efficacy of compounds was assayed on human triple negative breast cancer and transplantable sarcoma in rat. The cytotoxicity was accessed by MTT test, NR uptake, CV assay and double AO/PI staining. Experimental data revealed that Monensic acid and [Ln(Mon)3(H2O)3] possess concentration- and time-dependent activity, and express promising cytotoxic properties against human and rat permanent cancer cell lines.

Calcium Phosphate Incorporated Bacterial Cellulose-Polyvinylpyrrolidone Based Hydrogel Scaffold: Structural Property and Cell Viability Study for Bone Regeneration Application

This work focuses on the analysis of structural and functional properties of calcium phosphate (CaP) incorporated bacterial cellulose (BC)-polyvinylpyrrolidone (PVP) based hydrogel scaffolds referred to as “CaP/BC-PVP”. CaP is incorporated in the scaffolds in the form of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) in different concentrations (β-TCP: HA (w/w) = 20:80, 40:60, and 50:50). The scaffolds were characterized on the basis of porosity, thermal, biodegradation, mechanical, and cell viability/cytocompatibility properties. The structural properties of all the hydrogel scaffolds show significant porosity. The biodegradation of “CaP/BC-PVP” scaffold was evaluated following hydrolytic degradation. Weight loss profile, pH change, scanning electron microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) study confirm the significant degradability of the scaffolds. It is observed that a 50:50_CaP/BC-PVP scaffold has the highest degree of degradation. On the other hand, the compressive strengths of CaP/BC-PVP hydrogel scaffolds are found between 0.21 to 0.31 MPa, which is comparable with the human trabecular bone. The cell viability study is performed with a human osteosarcoma Saos-2 cell line, where significant cell viability is observed in all the hydrogel scaffolds. This indicated their ability to facilitate cell growth and cell proliferation. Considering all these substantial properties, CaP/BC-PVP hydrogel scaffolds can be suggested for detailed investigation in the context of bone regeneration application.

The Features of Family Relations of Adolescent Girls at Risk of Eating Disorders

The family risk factors of eating disorders (ED) of adolescent girls were studied. 376 girls aged 13 to 17 years from Ryazan city schools filled in Eating Attitude Test (EAT-26), CRPBI (E. Schaefer, Russian adaptation), Risk Factors of ED (T.A. Meshkova, research questionnaire). Comparison of the groups with upper and lower quartiles of EAT-26 scores demonstrates, that the families of the girls being at risk of ED are characterized by the authoritarian mother, who disregards of daughter's problems, and by the neutral position of the father.Parents more often were concerned about daughters’ figure, have a preoccupation with dieting. The girls of risk group have a fear of condemnation from family members, blaming for missteps. They have lack of praise for achievements, frequent bans and physical punishment, sense of dependency on family. It is possible, that daughter's eating disturbances reflect the some kind of protest and present a defensive reaction to the current family situation.

Metal Zn(II), Cu(II), Ni (II) complexes of ursodeoxycholic acid as putative anticancer agents

The aim of the study was to evaluate the influence of metal [Zn(II), Cu(II), Ni(II)] complexes with ursodeoxycholic acid (UDCA) on the viability and proliferation of tumour and non-tumour cells. Cell lines established from retrovirus-transformed chicken hepatoma (LSCC-SF-Mc29) and rat sarcoma (LSR-SF-SR) as well as from human cancers of the breast (MCF-7), uterine cervix (HeLa), lung (A549) and liver (HepG2) were used as model systems. Non-tumour human embryo (Lep-3) cells were also included in some of the experiments. The investigations were carried out by the thiazolyl blue tetrazolium bromide (MTT) test, neutral red uptake cytotoxicity assay, crystal violet staining, double staining with acridine orange and propidium iodide and the colony-forming method. The results obtained revealed that: (1) UDCA and its metal complexes in the tested concentrations decreased (to a varying degree) the viability and proliferation of the treated cells in a time- and concentration-dependent manner; (2) chicken hepatoma (LSCC-SF-Mc29) cells were most sensitive to the cytotoxic and antiproliferative action of the compounds tested, followed by rat sarcoma (LSR-SF-SR) cells; (3) Cu‒UDCA and Ni‒UDCA were more effective against animal LSCC-SF-Mc29 and LSR-SF-SR cells, while Zn‒UDCA significantly decreased the viability and proliferation of human tumour cell lines; (4) applied independently, UDCA expressed lower cytotoxic/cytostatic activity as compared to metal complexes; and (5) the sensitivity of the non-tumour embryonic Lep-3 cells to the effects of UDCA and its metal complexes was comparable or even higher than those of the human tumour cells.

Self-assembly of novel molecular complexes of 1,10-phenanthroline and 5-amino-1,10-phenanthroline and evaluation of their in vitro antitumour activity

Novel molecular complexes of 1,10-phenanthroline (phen) and 5-amino-1,10-phenanthroline (5-NH2-phen) [(5-NH2-phen)2(phen) (H2O)3 (1), (phen)2(imidazole) (H+) (BF4-) (2), (phen)2(benzimidazole) (H+) (BF4-) (3), (5-NH2-phen)4(H2O)3 (4), and (phen)3 (indole) (H+) (BF4-) (5)] were synthesized via self-assembly processes and their in vitro anticancer activity was investigated. The structures of the compounds were confirmed by UV, FTIR, CIMS(CH4) and elemental analysis. The crystal structure of 2 was determined by X-ray diffraction. Cytotoxicity of the substances was measured using the cultivated human tumour cell lines HepG2, HEp-2, and 8-MB-GA. The tested substances showed different activity depending on the cell line and amount used. Substances 2 and 3 were not toxic to the non-tumour cells (Lep-3), but significantly toxic to all tumour ones. This is not the case with compounds 4 and 5, which are non-toxic towards carcinogenic cell lines, but even stimulate both HepG2 and HEp-2.

Experimental strategies in gene therapy of cancer

Gene therapy is a new and innovative approach to the treatment of malignant neoplasms, although it is still not capable of eradicating cancer in humans. Selection of the appropriate vector with maximal efficiency and minimal toxicity is crucial for gene therapy and numerous viral and non-viral (synthetic) methods for gene transfer have been developed. There are different gene therapy approaches for cancer treatment such as: 1) gene correction; 2) molecular chemotherapy; 3) proapoptotic gene therapy; 4) antiangiogenic gene therapy; 5) immune gene therapy; and 6) modulation of drug resistance/sensitivity. Cancer gene therapy represents one of the most rapidly developing areas in preclinical and clinical research. However, some problems need to be solved to make sure this strategy is safe, effective and long-lasting before it becomes routinely adopted in clinical practice.

Alkaloids from the roots of Senecio macedonicus Griseb

The new alkaloids 7-,9-diangeloylplatynecine (1) and 8-episarracine N-oxide (2), were isolated and identified from the roots of Senecio macedonicus. Another one, 8-epineosarracine was detected by GC/MS analyses of the crude alkaloid mixture. The cytotoxicity and biological activity of the alkaloids were tested on normal murine spleen lymphocytes and P3U1 mouse myeloma.

Clustering of pedigrees using marker allele frequencies: impact on linkage analysis

Ethnicity may form the basis for locus heterogeneity at certain susceptibility loci for complex diseases. Classification of pedigrees into ethnic groups is usually based upon self-report, but this may not be sensitive or specific. We investigated whether it is possible to cluster families from an admixed population using pedigree-specific marker allele frequencies. We used 323 autosomal microsatellite markers from 216 pedigrees who described themselves as either Caucasian or African American. First, we compared the stated ethnicity of pedigrees with clusters using pedigree-specific marker allele frequencies as input for a self-organizing map, a type of neural network. Using data from different chromosomes, nine pedigrees which were self-reported as African American were clustered with the Caucasian pedigrees. Removal of these nine pedigrees from the African American group did not markedly affect linkage results. We then proceeded to determine whether there was further heterogeneity between pedigrees using 1 x 3 nodes. Forty-four pedigrees were clustered in a group intermediate to the African American or Caucasian clusters. This group was composed of 36 and 8 pedigrees that described themselves as African American and Caucasian, respectively. Linkage analysis was performed in this group and results compared with the groups based upon self-reported ethnicity. Linkage to a region on chromosome 3 was observed in this intermediate group, which was more significant than any of the results obtained when pedigrees were grouped using self-reported ethnicity. Use of marker data may assist in clustering pedigrees with similar, ethnic backgrounds and may increase the power for genetic linkage studies.

Investigations on the aminoacid content of tumor associated antigens of rat sarcoma cells induced by virus

In our previous work (Alexandrov et al., 1996) was reported that the rat sarcoma cells induced by SR-RSV express two tumor associated antigens (TAA). The one TAA has a molecular weight of 52 kD and is detected by the help of a monoclonal antibody 2C2 only on the outer side of the plasma membrane of the sarcoma cells. The other antigen, with molecular weight of 28 kD, is expressed on the outher and inner side of the membrane. The antigens were isolated as a pure fraction by polyacrylamide electrophoresis and prepared for aminoacid analysis after that. The consisting 16 bound aminoacids were in different amounts. Both antigens are rich in glycine and poor in aromatic and sulphur-containing aminoacids. The presence of glucosamine and galactosamine in the antigens proves their glycoprotein nature. The received data show that the both TAA-s differ not only in molecular weights, place of expression and functional activity, but also in the amount of the bound aminoacids which constitute their proteins.

Fluorescent and electron-microscopy immunoassays employing polyclonal and monoclonal antibodies for detection of goose parvovirus infection

Polyclonal antibodies (PAbs) raised in geese and eight mice hybridomas secreting monoclonal antibodies (MAbs) against the goose parvovirus (GPV) were prepared. They were used for development of immunofluorescence (IF) and immunoelectron-microscopic (IEM) techniques to demonstrate the GPV infection in infected organs and biological fluids. The GPV antigens were established by immunofluorescence within the nuclei and the cytoplasm of many infected cells of the chorioallantoic membrane of goose and Peckin duck embryos, liver and heart of mortally diseased goslings. By means of IEM it was possible to detect the GPV in native organ homogenate supernatants and allantoic fluids. All techniques used in the study could be successfully applied for rapid diagnosis of the GPV infection. The test systems on the basis of MAbs should, however, be preferred. By means of immunoblotting (IB) using PAbs and MAbs four viral proteins (VP) with MW 88, 77, 65 and 60 kDa were demonstrated. Contrary to the others the VP with MW 65 kDa was the most antigenically reactive though invisible in the SDS-PAGE and Coomassie-blue dye-stained preparations.

Domains in human interferon alpha-1 gene containing tandems of arginine codons AGG play the role of translational initiators in E. coli

The AGG and AGA are the least used arginine codons in E. coli but they are the most preferable ones in eukaryotes. The low expression of some eucaryotic genes (such as human alpha-1 interferon gene) which contain clusters of AGG codons is explained either by the limited pool of the tRNA(AGG) (Varenne and Lazdunski, 1986) or by the competition of these clusters with the Shine-Dalgarno (SD) sequence (Ivanov et al., 1992). The aim of the present study is to demonstrate the in vivo capacity of AGG tandems to bind to bacterial ribosomes. The two tandems of AGG codons (Arg12 Arg13 and Arg163 Arg164) of hIF alpha 1 with their surrounding nucleotides were cloned in a bacterial expression plasmid containing a strong promoter and a reporter gene (chloramphenicol acetyltransferase, CAT) devoid of a ribosome binding site. The results obtained showed that both AGG tandems initiated translation of the CAT mRNA with an efficiency equal to that of the consensus SD sequence and several fold higher than the native SD sequence of the CAT gene.

Expression of human alpha 1 interferon genes in vectors containing tandemly located promoters recognized by two different RNA polymerases (Escherichia coli and T7)

An expression vector containing two tandemly located promoters (T7 and P1) and two transcription terminators recognized by two different RNA polymerases (T7 RNA polymerase and Escherichia coli RNA polymerase) was constructed. Human alpha 1 interferon gene variants were cloned in this vector and their expression was studied in E. coli strains containing [E. coli BL2I (DE3)] or devoid (E. coli BL21) of the gene for the T7 RNA polymerase. We report that simultaneous activity of the two promoters reduces the level of gene expression when compared with the levels of expression corresponding to either P1 or T7 promoter alone.

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.

Effect of tandemly repeated AGG triplets on the translation of CAT-mRNA in E. coli

It has been shown that tandems of rare arginine codons AGG have a strong inhibitory effect on translation of mRNA in E. coli [5]. This has been explained by the rate-limiting interaction of these codons with the less abundant tRNA(AGG) [6]. In this study tandemly repeated AGG triplets were introduced into the chloramphenicol acetyltransferase (CAT) gene either upstream of the initiation ATG codon or downstream of it (both in frame and out of frame) and the expression of the modified genes was investigated. We report that the addition of AGG clusters resulted in a substantial inhibitory effect on CAT gene expression independently of their localization in mRNA. This inhibitory effect is explained by a competition of the tandem AGGAGG with the natural Shine-Dalgarno (SD) sequence (consensus AAGGAGGU) for the 3'-end of the 16S small ribosomal RNA (rRNA).