Biomedical subjects

S Nishimura

Publications and source records attributed to S Nishimura.

At least 937 records · Page 52Linked to original sources

PubMed1979

Structure of poly(adenosine diphosphate ribose): identification of 2'-[1''-ribosyl-2''-(or 3''-)(1'''-ribosyl)]adenosine-5',5'',5'''-tris(phosphate) as a branch linkage.

Poly([14C]adenosine diphosphate ribose) was synthesized from [14C]NAD+ with calf thymus nuclei. The fraction containing poly(adenosine diphosphate ribose) eluted with 0.22--0.40 M phosphate buffer (pH 6.8) from a hydroxylapatite column, was completely hydrolyzed with venom phosphodiesterase, and was separated by DEAE-Sephadex A-25 column chromatography in 7 M urea. A new compound, which constituted 2% of the products from poly(adenosine diphosphate ribose), was found in addition to the expected products--i.e., 5'-AMP, 2'-(1''-ribosyl)adenosine-5',5''-bis(phosphate), and its derivatives. This compound was identified as 2'-[1''-ribosyl 2''-(or 3''-)(1'''-ribosyl)]adenosine-5',5'',5'''-tris(phosphate). The existence of this compound is evidence of a branching structure of poly(adenosine diphosphate ribose), which was previously thought to be a linear molecule. The content of this compound suggests that the frequency of branching is about 1 per 20--30 adenosine diphosphate ribose residues of high molecular weight poly(adenosine diphosphate ribose).

Chemical Phenomena↗

PubMed1979

Sequence of the gene for isoleucine tRNA1 and the surrounding region in a ribosomal RNA operon of Escherichia coli.

A DNA fragment of about 2000 base pairs carrying the gene for tRNA(1) (Ile) has been cloned from a total Eco RI endonuclease digest of Escherichia coli DNA. Sequence analyses revealed that about the first 850 base pairs from one end of the fragment contain a nucleotide sequence corresponding to that in the 3'-end of 16S rRNA. The gene for tRNA(Ile) follows the 16S rRNA gene and both genes flank a spacer sequence of 68 base pairs. The spacer region contains a repeating, a hair pin and a symmetrical structure when the sequence is viewed in the single stranded form. A notable hair pin structure is also observed in the region adjacent to the 3'-end of the tRNA(1) (Ile) gene. In addition, about 850 base pairs from the other end of the DNA fragment have been found to contain the nucleotide sequence of the 5'-end of 23S rRNA. The presence of the genes for tRNA(1) (Ile), 16S and 23S rRNA and the hybridization to tRNA(1) (Ala) suggest that this cloned DNA is part of one of the E. coli rRNA operons carrying these two tRNA genes as a spacer.Images

Base Sequence↗

PubMed1979

Chemical modification study of aminoacyl-tRNA conformation.

Chemical reactivity of cytosines in 32P-labeled E. coli tRNA1Leu, E. coli tRNAPhe and yeast tRNAPhe before and after aminoacylation was examined by use of a cytosine-specific reagent, semicarbazide-bisulfite mixture. In all the three tRNA species examined, the cytosine residues that were susceptible to the modification were the same in the aminoacylated tRNA and the unacylated tRNA. Only a limited number of the cytosine residues were modifiable: those that occur in the anticodon, the 3'-CCA terminus, the D-loop, and the extra loop. The sites accessible by the reagent are in good agreement with the general three-dimensional structure of tRNA proposed in literature. These results indicate that the gross conformation of these tRNAs does not change on aminoacylation, and consequently favor the view that the T psi C(G) sequence could become exposed in later steps of protein synthesis in order to achieve the binding of aminoacyl tRNA to ribosomes.

Anticodon↗

PubMed1979

Isolation of hydroxy-Y base from rat liver tRNAPhe.

A Y-base derivative was isolated from rat liver tRNAPhe and its structure was assigned to be alpha-(carboxyamino)-beta-hydroxy-4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazol[1,2-a]purine-7-butyric acid dimethyl ester (hydroxy-Y), based on the results of mass spectrometry and chemical degradation. This modified base seems to be the major fluorescent component of rat liver tRNAPhe; the peroxy-Y base previously isolated from rat liver tRNAPhe and characterized by Nakanishi and his coworkers (1,2) was not present in our preparation.

Animals↗

PubMed1979

Nucleotide sequence of formylmethionine tRNA from an extreme thermophile, Thermus thermophilus HB8.

The nucleotide sequence of formylmethionine tRNA from an extreme thermophile, Thermus thermophilus HB8, was determined by a combination of classical methods using unlabeled samples to determine the sequences of the oligonucleotides of RNase T1 and RNase A digests and a rapid sequencing gel technique using 5'-32P labeled samples to determine overlapping sequences. Formylmethionine tRNA from T. thermophilus is composed of two species, tRNAf1Met and tRNAf2Met. Their nucleotide sequences are almost identical, and are also almost identical with that of E. coli tRNAfMet, except for slight modifications and replacements. Both species have modifications at three points which do not exist in E. coli tRNAfMet: 2'-O-methylation at G19, N-1-methylation at A59 and 2-thiolation at T55. Moreover U51 in E. coli tRNAfMet is replaced by C51 in both species, so that a G-C pair is formed between this C51 and G65. tRNAf2Met has a reversed G-C pair at positions 52 and 64 compared with those in tRNAf1Met and E. coli tRNAfMet. Other regions are mostly the same as those in all prokaryotic initiator tRNAs so far reported. The thermostability of these thermophile initiator tRNAs is discussed in relation to their unique modifications.

Base Sequence↗

PubMed1979

Occurrence of 1-methyladenosine and absence of ribothymidine in transfer ribonucleic acid of Mycobacterium smegmatis.

The minor base composition of Mycobacterium smegmatis tRNA has been studied. Thin-layer chromatographic patterns of a ribonuclease T2 digest of mycobacterial tRNA indicated the presence of appreciable amounts of 1-methyladenosine (which is commonly present only in eucaryotic tRNA), dihydrouridine, and 7-methylguanosine. Ribothymidine was absent. The S-adenosylmethionine-dependent tRNA methylases of M. smegmatis catalyzed the formation of 1-methyladenosine when Escherichia coli tRNA was used as acceptor. Similarly, E. coli extracts methylated the tRNA of M. smegmatis, forming ribothymidine.

Adenosine↗

PubMed1979

Sequential CT observations of irradiated intracranial germinomas.

Computed tomography (CT) has improved the accuracy of preoperative diagnosis of intracranial tumors. CT findings of germinoma are a mass of isodensity or of slightly increased density with significant, homogeneous enhancement after intravenous contrast injection. These findings are characteristic but not pathognomonic, and differential diagnosis from other solid tumors is not easy. Cerebrospinal fluid cytology and response to irradiation aid in this differential diagnosis. The nine cases of germinoma reported showed rapid response to irradiation even at small doses (600 rad), and complete disappearance of the mass on CT at 1,600--3,300 rad. Other radiosensitive masses to be differentiated in the pineal region are pinealocytoma or pinealoblastoma.

Adolescent↗

PubMed1979

Total removal of a parasagittal meningioma of the posterior third of the sagittal sinus and its repair by autogenous vein graft. Case report.

Total removal is reported of a parasaggital meningioma that invaded the lateral wall and lateral recess of the posterior third of the superior sagittal sinus. The operation was performed by using a silicone rubber non-collapsible tube with an inflatable balloon cuff at each end for the bypass of the sinus blood, and entailed repair of the defect in the sinus wall by a saphenous vein graft. The clinical results and angiographic findings are presented.

Brain↗

PubMed1979