[A Case of Extrahepatic Bile Duct Carcinoid Tumor Involving Diagnostic Difficulties].

A patient in his 60s had undergone laparoscopic anterior resection for the treatment of carcinoma of the rectum in February 2016. Histopathologic examination revealed the lesion as a pT2(MP)n(-)M0, fStage Ⅰrectal cancer. One year post-surgery, contrast-enhanced computed tomography(CT)revealed enhancement of parts of the intrapancreatic distal bile ducts. Magnetic resonance cholangiopancreatography(MRCP)showed filling defects at the same site. Magnetic resonance imaging( MRI)with an endorectal coil(ERC)was then performed to identify reproducible bile duct filling defects. Neither cytology nor biopsy yielded any findings that definitely indicated malignancy. Intraductal ultrasonography(IDUS)led to the suspicion of a nonepithelial tumor or an enlarged lymph node. Repeated biopsies via ERC were performed based on the absence of evidence of malignancy and revealed the presence of some atypical cells within the lesions. Although no definitive diagnosis could be made, the patient was scheduled for surgery in June 2017 after obtaining his consent. Upon taping of the common bile duct during surgery, a tumor was palpable on the dorsal aspect of the pancreas. The bile duct tumor was completely excised and submitted for intraoperative diagnosis; the pancreatic dorsal aspect appeared to be totally split. There was no evidence of atypia in the neoplasm, which was therefore considered to be benign; however, malignancy could not be completely ruled out because the patient had presented with elevated serum levels of carbohydrate antigen(CA)19-9 once before the operation. After intraoperative consultation with the patient's family members, who were reluctant to provide consent for pancreaticoduodenectomy, we completed the operation with resection of the bile duct tumor, followed by choledochojejunostomy. The tumor was found to be chromogranin A(+), cluster of differentiation(CD)56(+/-), CA19-9(+, solely ductal structure), carcinoembryonic antigen(CEA)(+, solely ductal structure), and intranuclear p53(-), with an MIB- 1 index of<2%. With regard to neuroendocrine markers, a region that could potentially have been a carcinoid tumor, based on the findings on hematoxylin and eosin(HE)staining, and a lumenized superficial region showed positivity in toto. Therefore, the lesion as a whole was diagnosed as a G1 carcinoid neuroendocrine tumor(NET). However, the superficial lumenized layer was positive for both CA19-9 and CEA; therefore, the tumor was thought to concurrently have epithelial characteristics. The lateral stumpwas negative, while the status of the ablated region remained unclear. After discussing the histopathologic examination results with the patient and his family members, the patient's follow-upwas decided to consist of periodic checkups without any further surgical intervention. The patient has since remained free of recurrence. Carcinoid tumor of the bile duct is extremely rare but should be considered in cases involving bile duct tumors that show enhancement on imaging prior to surgery and for which no definitive diagnosis can be established despite repeated biopsy explorations.

[A Case of Complete Response to Computed Tomography-Guided Celiac Plexus Neurolysis of Pain Associated with Postoperative Recurrence of Colon Cancer].

The patient was a man in his 40s, who had undergone laparoscopic ileocecal resection with lymph node dissection(D3)for cecal cancer in January 2012. Histopathological examination of the resected specimens had revealed StageⅡ primary tumor with subserosal invasion and positive metastasis in 1-3 regional lymph nodes(pT2[SS]n1[+]). The pathological stage was Ⅲa(fStage Ⅲa), and the tumor showed RAS gene mutation. The patient was administered 5 cycles of postoperative adjuvant chemotherapy with oral tegafur/uracil(UFT)in combination with calcium folinate(UZEL). Abdominal computed tomography( CT)performed 1.5 years postoperatively revealed liver metastasis, and a laparoscopic partial hepatectomy was performed in August 2015. In addition, a node in the greater omentum, located in the inferior surface of the liver, was also resected. Histopathological examination of the resected specimens revealed peritoneal metastasis, based on the identification of the same type of adenocarcinoma as the colon cancer. The patient was given 8 cycles of adjuvant chemotherapy with capecitabine and oxaliplatin(CapeOX). Then, he presented with colonic ileus, caused by recurrent dissemination, and underwent a laparoscopic transverse colectomy in October 2015. Multiple perineal disseminations were found intraoperatively, and chemotherapy was initiated with irinotecan plus tegafur/gimeracil/oteracil(S-1)plus bevacizumab(IRIS/BV)for the recurrent and unresectable disease. After 27 cycles of this regimen, lung metastasis was detected; in addition, progression of the para-aortic node metastasis around the celiac plexus was also observed, and the patient was considered as having pro- gressive disease(PD). Treatment with trifluridine/tipiracil(TAS102)was started in September 2017. Prior to the initiation of this regimen, the dose of opioid rescue medication previously started for back and abdominal pain was rapidly increased. Accordingly, the base dose was increased, but the pain could not be controlled, and the major pain was consistently located along the area of innervation in the celiac plexus. Therefore, celiac plexus neurolysis(CPN)was performed as a local therapy. A CT-guided injection technique was used to administer urografin, bupivacaine, and absolute ethanol to complete the procedure. The patient was discharged without major complications, and the base opioid dose was gradually reduced. Since the patient did not require any rescue medication during daytime on some days, the reduction of the base opioid dose was significantly effective in improving the patient's quality of life(QOL). In patients with pain possibly caused by metastasis to the para-aortic nodes, this local therapy technique may be considered.

[A Case of Advanced Breast Cancer in Which Marked Improvement of Joint Pain Was Obtained with Stepwise Dose Reduction of Trastuzumab Emtansine (T-DM1)].

A 51-year-old woman had previously received treatment for breast cancer at another hospital but had refused early and aggressive treatment. Therefore, she was treated with symptomatic therapy. As her disease progressed, the patient wished to receive palliative care, and was transferred to a palliative care hospital. However, based on her general condition, it was determined that aggressive treatment should not be abandoned, and she was referred to our hospital for treatment. During her initial visit, the patient was found to have left breast cancer with chest wall invasion, right breast metastasis, multiple liver and lung metastases, left pleural effusion accompanied by pleural dissemination, and left upper limb edema. There was no evidence of bone metastases. The patient's pain was managed with oral oxycodone sustained-release tablets (320 mg daily), using high-dose (80 mg) oral oxycodone hydrochloride hydrate as rescue medication. The results of immunohistochemical testing, confirmed by her previous hospital, were ER (-), PgR (-) and HER2/neu positive. First-line treatment was initiated with paclitaxel (PTX) plus trastuzumab (Tmab), and the response was rated as stable disease (SD). During the course of treatment, she developed drug-induced interstitial pneumonia, which was probably caused by the taxane. Therefore, the first-line treatment was discontinued and T-DM1 was initiated as second-line treatment. However, beginning with cycle 3 of the T-DM1 treatment, the patient began complaining of joint pain, mainly in the upper limbs. Therefore, the dose of oxycodone sustained-release tablets was increased to 600 mg per day. However, the patient's joint pain showed no improvement and it was considered unlikely that the pain was due to bone metastases. It was suspected that the pain was an adverse reaction to T-DM1, and the dose of T-DM1 was reduced by one step in cycle 7 of treatment. This resulted in a dramatic improvement of the patient's symptoms. Since oxycodone sustained-release tablets was being used at a high dose, sleepiness caused by the drug interfered with her activities of daily living. Consequently, as part of an opioid rotation scheme, topical fentanyl citrate was used concomitantly, and the initial daily oxycodone sustained-release tablets dose of 600 mg was reduced to 40 mg and administered in combination with fentanyl citrate (12mg). These findings suggest that uncontrollable joint pain can occur as an adverse reaction to T-DM1.

Histochemical study of trans-polyisoprene accumulation by spectral confocal laser scanning microscopy and a specific dye showing fluorescence solvatochromism in the rubber-producing plant, Eucommia ulmoides Oliver.

A microscopic technique combining spectral confocal laser scanning microscopy with a lipophilic fluorescent dye, Nile red, which can emit trans-polyisoprene specific fluorescence, was developed, and unmixed images of synthesized trans-polyisoprene in situ in Eucommia ulmoides were successfully obtained. The images showed that trans-polyisoprene was initially synthesized as granules in non-articulated laticifers that changed shape to fibers during laticifer maturation. Non-articulated laticifers are developed from single laticiferous cells, which are differentiated from surrounding parenchyma cells in the cambium. Therefore, these observations suggested that trans-polyisoprene biosynthesis first started in laticifer cells as granules and then the granules accumulated and fused in the inner space of the laticifers over time. Finally, laticifers were filled with the synthesized trans-polyisoprene, which formed a fibrous structure fitting the laticifers shape. Both trans- and cis-polyisoprene are among the most important polymers naturally produced by plants, and this microscopic technique combined with histological study should provide useful information in the fields of plant histology, bioindustry and phytochemistry.

Overexpression of an isopentenyl diphosphate isomerase gene to enhance trans-polyisoprene production in Eucommia ulmoides Oliver.

BACKGROUND: Natural rubber produced by plants, known as polyisoprene, is the most widely used isoprenoid polymer. Plant polyisoprenes can be classified into two types; cis-polyisoprene and trans-polyisoprene, depending on the type of polymerization of the isoprene unit. More than 2000 species of higher plants produce latex consisting of cis-polyisoprene. Hevea brasiliensis (rubber tree) produces cis-polyisoprene, and is the key source of commercial rubber. In contrast, relatively few plant species produce trans-polyisoprene. Currently, trans-polyisoprene is mainly produced synthetically, and no plant species is used for its commercial production. RESULTS: To develop a plant-based system suitable for large-scale production of trans-polyisoprene, we selected a trans-polyisoprene-producing plant, Eucommia ulmoides Oliver, as the target for genetic transformation. A full-length cDNA (designated as EuIPI, Accession No. AB041629) encoding isopentenyl diphosphate isomerase (IPI) was isolated from E. ulmoides. EuIPI consisted of 1028 bp with a 675-bp open reading frame encoding a protein with 224 amino acid residues. EuIPI shared high identity with other plant IPIs, and the recombinant protein expressed in Escherichia coli showed IPI enzymatic activity in vitro. EuIPI was introduced into E. ulmoides via Agrobacterium-mediated transformation. Transgenic lines of E. ulmoides overexpressing EuIPI showed increased EuIPI expression (up to 19-fold that of the wild-type) and a 3- to 4-fold increase in the total content of trans-polyisoprenes, compared with the wild-type (non-transgenic root line) control. CONCLUSIONS: Increasing the expression level of EuIPI by overexpression increased accumulation of trans-polyisoprenes in transgenic E. ulmoides. IPI catalyzes the conversion of isopentenyl diphosphate to its highly electrophilic isomer, dimethylallyl diphosphate, which is the first step in the biosynthesis of all isoprenoids, including polyisoprene. Our results demonstrated that regulation of IPI expression is a key target for efficient production of trans-polyisoprene in E. ulmoides.

Effect of Alkyl Chain Length of N-Alkyl-N'-(2-benzylphenyl)ureas on Gelation.

Urea derivatives that were substituted with a 2-benzylphenyl group and an alkyl group functioned as low molecular weight gelators for various organic solvents and ionic liquids. Urea derivatives with long alkyl chains were effective for the gelation of polar solvents. However, they were not suitable for the gelation of non-polar solvents, whereas urea derivatives with short alkyl chains were effective. Ionic liquids were similar to polar solvents in that urea derivatives with long alkyl chains were the most effective gelators. The physical properties of the formed supramolecular gels were analyzed by dynamic viscoelasticity measurements using a rheometer.

Fluorescent probing for RNA molecules by an unnatural base-pair system.

Fluorescent labeling of nucleic acids is widely used in basic research and medical applications. We describe the efficient site-specific incorporation of a fluorescent base analog, 2-amino-6-(2-thienyl)purine (s), into RNA by transcription mediated by an unnatural base pair between s and pyrrole-2-carbaldehyde (Pa). The ribonucleoside 5'-triphosphate of s was site-specifically incorporated into RNA, by T7 RNA polymerase, opposite Pa in DNA templates. The fluorescent intensity of s in RNA molecules changes according to the structural environment. The site-specific s labeling of RNA hairpins and tRNA molecules provided characteristic fluorescent profiles, depending on the labeling sites, temperature and Mg2+ concentration. The Pa-containing DNA templates can be amplified by PCR using 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds), another pairing partner of Pa. This site-specific fluorescent probing by the unnatural pair system including the s-Pa and Ds-Pa pairs provides a powerful tool for studying the dynamics of the local structural features of 3D RNA molecules and their intra- and intermolecular interactions.

3'-Azido-2',3'-dideoxynucleoside 5'-triphosphates inhibit telomerase activity in vitro, and the corresponding nucleosides cause telomere shortening in human HL60 cells.

Telomerase adds telomeric DNA repeats to the ends of linear chromosomal DNA. 3'-Azido-3'-deoxythymidine 5'-triphosphate (AZTTP) is a known telomerase inhibitor. To obtain more selective and potent inhibitors that can be employed as tools for studying telomerase, we investigated the telomerase-inhibitory effects of purine nucleosides bearing a 3'-down azido group: 3'-azido-2',3'-dideoxyguanosine (AZddG) 5'-triphosphate (AZddGTP), 3'-azido-2',3'-dideoxy-6-thioguanosine (AZddSG) 5'-triphosphate (AZddSGTP), 3'-azido-2',3'-dideoxyadenosine (AZddA) 5'-triphosphate (AZddATP) and 3'-azido-2',3'-dideoxy-2-aminoadenosine (AZddAA) 5'-triphosphate (AZddAATP). Of these, AZddGTP showed the most potent inhibitory activity against HeLa cell telomerase. AZddGTP was significantly incorporated into the 3'-terminus of DNA by partially purified telomerase. However, AZddGTP did not exhibit significant inhibitory activity against DNA polymerases alpha and delta, suggesting that AZddGTP is a selective inhibitor of telomerase. We also investigated whether long-term treatment with these nucleosides could alter telomere length and growth rates of human HL60 cells in culture. Southern hybridization analysis of genomic DNA prepared from cells cultured in the presence of AZddG and AZddAA revealed reproducible telomere shortening.

Phosphoserine aminoacylation of tRNA bearing an unnatural base anticodon.

An unnatural base pair between 7-(2-thienyl)-imidazo[4,5-b]pyridine (Ds) and pyrrole-2-carbaldehyde (Pa) could expand the genetic alphabet and allow the incorporation of non-standard amino acids into proteins at defined positions. For this purpose, we synthesized tRNAs bearing Pa at the anticodon and tested non-standard amino acid phosphoserine aminoacylation by the wild-type and various engineered phosphoseryl-tRNA synthetases (SepRSs). The D418N D420N T423V triple mutant of SepRS efficiently charged phosphoserine to tRNA containing the PaUA anticodon with a K(m)=47.1muM and a k(cat)=0.151s(-1), which are comparable to the values of the wild-type SepRS for its cognate substrate, tRNA(Cys) with the GCA anticodon (26.9muM and 0.111s(-1)). The triple mutant SepRS and the tRNA with the PaUA anticodon represent a specific pair for the site-specific incorporation of phosphoserine into proteins in response to the UADs codon within mRNA.

An unnatural base pair system for in vitro replication and transcription.

The development of unnatural base pairs that function in replication, transcription, and translation could expand the genetic alphabet and enable the site-specific incorporation of functional components into nucleic acids and proteins. We present an unnatural base pair between 7-(2-thienyl)-imidazo[4,5-b]pyridine (denoted by Ds) and pyrrole-2-carbaldehyde (denoted by Pa). In replication, the Ds-Pa pair exhibits high selectivity in combination with the usual and modified triphosphate substrates and exonuclease-proficient DNA polymerases. In transcription, the Ds-Pa pair mediates the site-specific incorporation of the substrates of both Ds and Pa into RNA by T7 RNA polymerase. This unnatural base pair system could facilitate the specific incorporation of functional components into RNA molecules at desired positions using DNA templates containing the unnatural base pair, which can be amplified by PCR.

An unnatural hydrophobic base pair system: site-specific incorporation of nucleotide analogs into DNA and RNA.

Methods for the site-specific incorporation of extra components into nucleic acids can be powerful tools for creating DNA and RNA molecules with increased functionality. We present an unnatural base pair system in which DNA containing an unnatural base pair can be amplified and function as a template for the site-specific incorporation of base analog substrates into RNA via transcription. The unnatural base pair is formed by specific hydrophobic shape complementation between the bases, but lacks hydrogen bonding interactions. In replication, this unnatural base pair exhibits high selectivity in combination with the usual triphosphates and modified triphosphates, gamma-amidotriphosphates, as substrates of 3' to 5' exonuclease-proficient DNA polymerases, allowing PCR amplification. In transcription, the unnatural base pair complementarity mediates the incorporation of these base substrates and their analogs, such as a biotinylated substrate, into RNA by T7 RNA polymerase (RNAP). With this system, functional components can be site-specifically incorporated into a large RNA molecule.

An efficient unnatural base pair for a base-pair-expanded transcription system.

For the site-specific incorporation of artificial components into RNA by transcription, an efficient, unnatural base pair between 2-amino-6-(2-thiazolyl)purine (denoted as v) and 2-oxo(1H)pyridine (denoted as y) was developed. The substrates of y and 5-substituted y were site-specifically incorporated into RNA by T7 RNA polymerase opposite v in templates. The efficiency and fidelity of the v-y pairing in transcription were as high as those of the natural A-T(U) and G-C pairings. Furthermore, RNAs containing two adjacent y bases were also transcribed from DNA templates containing two v bases. This specific transcription allows the large-scale preparation of artificial RNAs and can be combined with other systems to simultaneously incorporate several different components into a transcript.

Site-specific incorporation of fluorescent probes into RNA by specific transcription using unnatural base pairs.

To analyze the local conformational changes of RNA molecules, we developed a site-specific fluorescent labeling method for RNA fragments by T7 transcription, using unnatural base pairs between 2-amino-6-(2-thienyl)purine (s) and 2-oxo(1H)pyridine (y) and between 2-amino-6-(2-thiazolyl)purine (v) and y. Ribonucleoside 5'-triphosphates of 5-fluorescence-linked y derivatives can be site-specifically incorporated into RNA, opposite s or v in DNA templates, by T7 RNA polymerase. Using this specific transcription, the substrate of a fluorescein-linked y was introduced into a theophylline-binding RNA aptamer. The replacement of U6 by the fluorescein-linked y maintained both the binding ability and selectivity of the aptamer to theophylline. Furthermore, the fluorescence intensity was increased upon theophylline binding, but was not changed by the addition of caffeine.

A two-unnatural-base-pair system toward the expansion of the genetic code.

Toward the site-specific incorporation of amino acid analogues into proteins, a two-unnatural-base-pair system was developed for coupled transcription-translation systems with the expanded genetic code. A previously designed unnatural base pair between 2-amino-6-(2-thienyl)purine (denoted by s) and pyridin-2-one (denoted by y) was used for the site-specific incorporation of yTP into RNA opposite s in templates by T7 RNA polymerase. For the site-specific incorporation of sTP into RNA, a newly developed unnatural base, imidazolin-2-one (denoted by z), is superior to y as a template base for pairing with s in T7 transcription. The combination of the s-y and s-z pairs provides a powerful tool to prepare both y-containing mRNA and s-containing tRNA for efficient coupled transcription-translation systems, in which the genetic code is expanded by the codon-anticodon interactions mediated by the s-y pair. In addition, the nucleoside of s is strongly fluorescent, and thus the s-z pair enables the site-specific fluorescent labeling of RNA molecules. These unnatural-base-pair studies provide valuable information for understanding the mechanisms of replication and transcription.

An unnatural base pair for efficient incorporation of nucleotide analogs into RNAs.

An unnatural base, 2-amino-6-(2-thiazolyl)purine (denoted as v), was developed as an efficient complementary base of another unnatural base, 2-oxo(1H)pyridine (denoted as y). The nucleoside derivatives of v and DNA fragments containing v were chemically synthesized. The efficiency and selectivity of the v-y pairing in replication and transcription were examined and compared to those of a previously developed unnatural base pair between 2-amino-6-(2-thienyl)purine (s) and y. The nucleoside 5'-triphosphate of y (dyTP or yTP) was selectively and efficiently incorporated into DNA or RNA opposite v. The efficiency of the v-y pairing was much higher than that of the s-y pairing. The unnatural v-y pair could be useful for large-scale preparations of RNA molecules containing unnatural bases at desired positions for the expansion of the genetic alphabet.

An unnatural base pair between imidazolin-2-one and 2-amino-6-(2-thienyl)purine in replication and transcription.

Nucleosides of imidazolin-2-one (designated by z) were designed and synthesized as pairing partners of 2-amino-6-(2-thienyl)purine (designated by s). Previously, we developed an unnatural base pair between s and pyridine-2-one (designated by y), and polymerases specifically incorporated the substrate of y into DNA and RNA opposite s in templates. Although s was efficiently incorporated opposite y, A was also incorporated opposite y with high efficiency. The replacement of y by z effectively improved the incorporation selectivity of s. The incorporation efficiency of A opposite z decreased, but the efficient incorporation of s opposite z was maintained as compared to that of the s-y pairing.

In vitro selection of RNA aptamers that bind to colicin E3 and structurally resemble the decoding site of 16S ribosomal RNA.

Colicin E3 is a ribonuclease that specifically cleaves at the site after A1493 of 16S rRNA in Escherichia coli ribosomes, thus inactivating translation. To analyze the interaction between colicin E3 and 16S rRNA, we used in vitro selection to isolate RNA ligands (aptamers) that bind to the C-terminal ribonuclease domain of colicin E3, from a degenerate RNA pool. Although the aptamers were not digested by colicin E3, they specifically bound to the protein (K(d) = 2-14 nM) and prevented the 16S rRNA cleavage by the C-terminal ribonuclease domain. Among these aptamers, aptamer F2-1 has a sequence similar to that of the region around the cleavage site from residue 1484 to 1506, including the decoding site, of E. coli 16S rRNA. The secondary structure of aptamer F2-1 was determined by the base pair covariation among the variants obtained by a second in vitro selection, using a doped RNA pool based on the aptamer F2-1 sequence. The sequence and structural similarities between the aptamers and 16S rRNA provide insights into the recognition of colicin E3 by this specific 16S rRNA region.

Enzymatic incorporation of an unnatural base pair between 4-propynyl-pyrrole-2-carbaldehyde and 9-methyl-imidazo [(4,5)-b]pyridine into nucleic acids.

A hydrophobic unnatural nucleoside of 4-propynylpyrrole-2-carbaldehyde (designated as Pa') was synthesized to improve its affinity with a pairing partner, 9-methyl-imidazo[(4,5)-b]pyridine (Q), in enzymatic incorporation. In single-nucleotide insertion experiments using the Klenow fragment, the substrate of Pa' (dPa'TP) was efficiently incorporated opposite Q in the template strand, as compared to the incorporation of pyrrole-2-carbaldehyde (dPaTP), which was previously developed.

Telomere shortening in human HL60 cells by treatment with deoxyguanosine analogs.

Telomerase is a cellular endogenous reverse transcriptase thought to play an important role in the maintenance of telomere length. We investigated the effects of 3'-azido-2',3'-dideoxyguanosine (AZddG) and carbocyclic oxetanocin G (C.OXT-G), of which the triphosphate derivatives AZddGTP and C.OXT-GTP show potent telomerase inhibition, on telomere length of human HL60 cells in culture. Although AZddG caused more significant telomere shortening than C.OXT-G, only a slight decrease of cell growth rate was observed.

An engineered Escherichia coli tyrosyl-tRNA synthetase for site-specific incorporation of an unnatural amino acid into proteins in eukaryotic translation and its application in a wheat germ cell-free system.

Tyrosyl-tRNA synthetase (TyrRS) from Escherichia coli was engineered to preferentially recognize 3-iodo-L-tyrosine rather than L-tyrosine for the site-specific incorporation of 3-iodo-L-tyrosine into proteins in eukaryotic translation systems. The wild-type TyrRS does not recognize 3-iodo-L-tyrosine, because of the bulky iodine substitution. On the basis of the reported crystal structure of Bacillus stearothermophilus TyrRS, three residues, Y37, Q179, and Q195, in the L-tyrosine-binding site were chosen for mutagenesis. Thirty-four single amino acid replacements and 16 of their combinations were screened by in vitro biochemical assays. A combination of the Y37V and Q195C mutations changed the amino acid specificity in such a way that the variant TyrRS activates 3-iodo-L-tyrosine 10-fold more efficiently than L-tyrosine. This engineered enzyme, TyrRS(V37C195), was tested for use in the wheat germ cell-free translation system, which has recently been significantly improved, and is now as productive as conventional recombinant systems. During the translation in the wheat germ system, an E. coli suppressor tRNA(Tyr) was not aminoacylated by the wheat germ enzymes, but was aminoacylated by the E. coli TyrRS(V37C195) variant with 3-iodo-l-tyrosine. After the use of the 3-iodotyrosyl-tRNA in translation, the resultant uncharged tRNA could be aminoacylated again in the system. A mass spectrometric analysis of the produced protein revealed that more than 95% of the amino acids incorporated for an amber codon were iodotyrosine, whose concentration was only twice that of L-tyrosine in the translation. Therefore, the variant enzyme, 3-iodo-L-tyrosine, and the suppressor tRNA can serve as an additional set orthogonal to the 20 endogenous sets in eukaryotic in vitro translation systems.