CT after Endovascular Repair of Abdominal Aortic Aneurysms: Diagnostic Accuracy of Diameter Measurements for the Detection of Aneurysm Sac Enlargement.

PURPOSE: To evaluate the diagnostic accuracy of diameter measurements for the detection of aneurysm volume increase during follow-up after endovascular aortic repair (EVAR) of abdominal aortic aneurysms (AAAs). MATERIALS AND METHODS: This retrospective study analyzed 100 pairs of follow-up computed tomography scans randomly selected from an EVAR database (male/female ratio, 91/9; mean age, 71 y; bifurcated and aortouniiliac stent grafts, 96% and 4%, respectively; mean interval, 359 d). Five maximum diameter (Dmax) values were measured (anteroposterior, transverse, axial, coronal, and perpendicular). Aneurysm sac volume was measured by manual segmentation and used as the standard of reference. Overall, 37% of patients had a persistent type II endoleak. RESULTS: The anteroposterior, transverse, axial, coronal, and perpendicular Dmax values increased in 39 patients (mean, 4.3 mm), 30 patients (mean, 4.0), 35 patients (mean, 3.9 mm), 43 patients (mean, 3.9 mm), and 41 patients (mean, 4.3 mm), respectively. Aneurysm sac volume increased in 39 patients (mean, 25.7 cm3). The cutoff levels according to the reporting standard for aneurysm sac enlargement (diameter ≥ 5.0 mm, volume ≥ 5.0%) had sensitivity/specificity rates of 29%/95%, 33%/97%, 29%/99%, 33%/93%, and 38%/96%, respectively, for the five Dmax values. The reference standards failed to detect aneurysm volume increase in 72%, 67%, 72%, 61%, and 67% of patients, respectively, with persistent type II endoleak. CONCLUSIONS: Depending on the chosen cutoff value, diameter measurements showed low to moderate sensitivity for the detection of aneurysm volume increase. The diameter measurements failed to detect aneurysm enlargement in a large number of patients with persistent type II endoleak after EVAR of AAA.

Toward understanding phosphoseryl-tRNACys formation: the crystal structure of Methanococcus maripaludis phosphoseryl-tRNA synthetase.

A number of archaeal organisms generate Cys-tRNA(Cys) in a two-step pathway, first charging phosphoserine (Sep) onto tRNA(Cys) and subsequently converting it to Cys-tRNA(Cys). We have determined, at 3.2-A resolution, the structure of the Methanococcus maripaludis phosphoseryl-tRNA synthetase (SepRS), which catalyzes the first step of this pathway. The structure shows that SepRS is a class II, alpha(4) synthetase whose quaternary structure arrangement of subunits closely resembles that of the heterotetrameric (alphabeta)(2) phenylalanyl-tRNA synthetase (PheRS). Homology modeling of a tRNA complex indicates that, in contrast to PheRS, a single monomer in the SepRS tetramer may recognize both the acceptor terminus and anticodon of a tRNA substrate. Using a complex with tungstate as a marker for the position of the phosphate moiety of Sep, we suggest that SepRS and PheRS bind their respective amino acid substrates in dissimilar orientations by using different residues.

Emergence of the universal genetic code imprinted in an RNA record.

The molecular basis of the genetic code manifests itself in the interaction of the aminoacyl-tRNA synthetases and their cognate tRNAs. The fundamental biological question regarding these enzymes' role in the evolution of the genetic code remains open. Here we probe this question in a system in which the same tRNA species is aminoacylated by two unrelated synthetases. Should this tRNA possess major identity elements common to both enzymes, this would favor a scenario where the aminoacyl-tRNA synthetases evolved in the context of preestablished tRNA identity, i.e., after the universal genetic code emerged. An experimental system is provided by the recently discovered O-phosphoseryl-tRNA synthetase (SepRS), which acylates tRNA(Cys) with phosphoserine (Sep), and the well known cysteinyl-tRNA synthetase, which charges the same tRNA with cysteine. We determined the identity elements of Methanocaldococcus jannaschii tRNA(Cys) in the aminoacylation reaction for the two Methanococcus maripaludis synthetases SepRS (forming Sep-tRNA(Cys)) and cysteinyl-tRNA synthetase (forming Cys-tRNA(Cys)). The major elements, the discriminator base and the three anticodon bases, are shared by both tRNA synthetases. An evolutionary analysis of archaeal, bacterial, and eukaryotic tRNA(Cys) sequences predicted additional SepRS-specific minor identity elements (G37, A47, and A59) and suggested the dominance of vertical inheritance for tRNA(Cys) from a single common ancestor. Transplantation of the identified identity elements into the Escherichia coli tRNA(Gly) scaffold endowed facile phosphoserylation activity on the resulting chimera. Thus, tRNA(Cys) identity is an ancient RNA record that depicts the emergence of the universal genetic code before the evolution of the modern aminoacylation systems.