The DNA fragment d(CpGpCpGpCpG) crystallises as a left-handed double helical molecule with Watson-Crick base pairs and an antiparallel organisation of the sugar phosphate chains. The helix has two nucleotides in the asymmetric unit and contains twelve base pairs per turn. It differs significantly from right-handed B-DNA.

Graft inclusion and vessel reattachment to openings made in the graft were employed in the treatment of 605 patients with thoracoabdominal aortic aneurysms. These patients were divided into four groups on the basis of the extent of aneurysm. Group I consisted of those patients with involvement of most of the descending thoracic and upper abdominal aorta; group II involved most of the descending thoracic aorta and most or all of the abdominal aorta; group III involved the distal descending thoracic aorta and varying segments of abdominal aorta; and group IV involved most or all of the abdominal aorta including the segment from which the visceral vessels arose. The cause of aneurysm formation was medial degenerative disease in 80%, and dissection in 17%; other causes were responsible in the remaining 3%. The median age was 65 years and associated diseases including aneurysms involving other segments, atherosclerotic occlusive disease, heart disease, chronic obstructive pulmonary disease (COPD), hypertension, and renal insufficiency were frequent. The aneurysm was symptomatic in 70% of cases and rupture had occurred in 4% of cases. There were 54 (8.9%) early (30-day) deaths and 151 late deaths; 400 (66%) patients were still alive 3 months to 20 years after operation, including 60% at 5 years. Statistically significant pre- and intraoperative variables by univariate analysis that were predictive of increased risk of early death were advancing age, associated diseases that included COPD, renal artery occlusive disease, atherosclerotic heart disease, renal insufficiency, and long aortic clamp time. Three of these (age, clamp time, and the presence of COPD) retained significance by multivariate analysis. Variables predictive of risk of late death were age, dissection, extent of aneurysm, rupture, heart disease, cerebrovascular disease, COPD, hypertension, and poor renal function. Age, rupture, renal dysfunction, extent of aneurysm, and dissection retained their significance by multivariate analysis. Variables predictive of neurologic disturbances of the lower extremities included rupture, reattachment of intercostal and lumbar arteries, clamp time, dissection, extent and age. Rupture, reattachment of vessels, dissection, and extent of aneurysm retained significance by multivariate analysis. Thus, the risk of this complication was greatest in patients with extensive lesions (group II) with aortic dissection. The greatest risk of renal failure after operation that required dialysis was in patients who had impaired renal function before operation. Methods employed did not prevent these complications.

The reverse turn, involving four consecutive amino acids, as a tertiary conformation in globular proteins is defined in terms of dihedral angles, the Ci... C.C4 distance and the 0 ... H-N4 hydrogen bond distance. In seven proteins we find 125 examples of turns, comprising 33% of the amino acids in these proteins, as compared with 34% of the residues forming helices and only 17% forming 3-sheets. The amino-acid compositions of turns, helices, and ,8-sheets are analyzed in some detail. We find Asn and Gly mainly in turns, Pro in turns (and at the beginning of helices), and Glu in helices. In these turns a statistical survey indicates that 19% of Asp residues are in the first position, 33% of Pro residues are in the second position, 24% of Asn residues are in the third position, and 26% of Trp residues are in the fourth position.Even though it has been 13 years since the first structure of a globular protein was determined to atomic resolution, we still do not know h9w the amino-acid sequence helps to determine the tertiary structure of a protein. However, the characterization by Venkatachalam (1) of the types of turns in polypeptide chains may aid in making predictions about the structure of proteins. These conformations, which we will call reverse turns, involve a nearly 1800 reversal of the peptide chain with a hydrogen bond between the CO group of residue i and the NH group of residue i + 3. One turn thus comprises four amino-acid residues and therefore contains a large amount of structural information in a short region of the polypeptide chain. When we analyzed the atomic coordinates of seven globular proteins, we found that a third of the amino-acid residues lie in turns. Moreover, about 50% of certain residues, such as Asn, Gly and Pro, are found in turns, and these residues have a low frequency of occurrence in helices or g-sheets. In the first section of this paper we describe certain criteria for the reverse turn and give a usable definition of it. In the second section we analyze the aminoacid composition of turns, helices, and sheets in globular proteins. Reverse turnsVenkatachalam studied the general conformations of three linked peptide units having hydrogen bonding between the first and third units. He found three general types-one helical and two nonhelical. The helical type, which he called type III, is part of a 31o helix, while the nonhelical types, type I and type II, involve a reversal in the direction of the peptide chain. As can be seen from the schematic drawings in Fig. 1, types I and II are related by a 1800 twist in the second peptide unit. The three types are characterized by the dihedral angles of the second and third residues. A listing of the allowed angles in the order (4)2, 2;

This report concerns 30 patients with the acute form of "inflammatory aneurysm" of the aorta treated during a 27-year period between April 1957 and March 1984. There were 28 men and two women whose ages ranged from 46 to 78 years (most over 60 years). All were heavy smokers. The aneurysmal disease was located below the renal arteries and the inflammatory changes were limited to the abdomen in 24 patients; one patient had a ruptured aneurysm. The aneurysm involved the entire abdominal aorta in one, the descending thoracic and infrarenal abdominal aorta in two, and the descending thoracic and abdominal aorta in continuity in three patients. The inflammatory changes occurred grossly and microscopically in both abdominal and thoracic aortic segments in five of the latter six patients. The changes were manifested by anterior and lateral mural inflammatory thickening contiguous with similar changes of the retroperitoneum and mediastinum that produced varying degrees of ureteral obstruction in seven patients. Most had abdominal, back, or flank pain and abdominal tenderness, suggesting rupture or leakage. Emergency exploratory operation had been performed elsewhere in 10 patients. Operation was abandoned because of exposure difficulties, bowel perforation, or visceral arterial involvement. Diagnosis was suggested by CT scan in 10, ultrasonography in one, and excretory urograms in seven patients. Treatment consisted of thoracoabdominal aortic replacement in six and infrarenal aortic replacement in 24. The aorta was clamped at the diaphragm in most of the latter cases to avoid injury to adjacent structures. Nephrectomy or ureterolysis was rarely necessary. Of these 30 patients, 29 were early (30 day) survivors and ureteral obstruction spontaneously subsided in most cases without special treatment. There was one late death at 2 months and eight deaths from 3 to 13 years; 20 (67%) patients are still alive.

ABST4RACTThe structure of the tetramer d(CpGpCpG) has been solved by x-ray analysis in two different crystal forms with and without spermine cations. The molecules crystallize in hexagonal unit cells and they form a left-handed double helix of Z-DNA similar to that previously reported for the hexamer d(Cp~pCpGpCpG). In the crystal lattice the molecules stack together to form a virtually continuous left-handed double helix in which every fourth phosphate group is missing. The stacking of bases upon each other is similar to that seen in the hexamer. However, the base pairs have a slightly different orientation in that the cytosine residues are slightly removed from the axis of the molecule compared to the position they occupy in the hexamer. The structures are similar in two crystal forms with and without spermine cations. Most of our earlier knowledge of the organization of the DNA double helix came from fiber x-ray diffraction studies. These studies had the advantage that diffraction data are relatively easy to obtain but they had the substantial disadvantage that the data are limited in resolution and consequently the finer structural details are lost. It has been apparent for at least 7 years that fragments of nucleic acid double helices can be seen in a single crystal diffraction analysis which, in principle, can lead to atomic resolution data (1, 2). Our (Table 1). In addition, a fiber diffraction pattern of poly(dG-dC) has yielded a pattern consistent with a polymeric version of Z-DNA (7). In all of the crystals we find some slight modifications in the basic geometry of the left-handed helix. These variations can be seen because of the relatively high resolution of the crystal diffraction data. This emphasizes the fact that there is configurational variability in the left-handed double helix, a variability which no doubt will eventually be found when right-handed double-helical DNA is studied by these same methods. A major biological feature of double-helical DNA involves its interactions with small molecules and ions as well as with proteins, and all of these are likely to induce variations in conformation. Many of these configurational variations are sequence-dependent and therefore reflect the informational content of these long molecules. EXPERIMENTAL METHODSThe ammonium salt of the deoxy tetramer d(CpGpCpG), designated d(CG)2, was prepared by modification of the recently developed phosphotriester method (8,9). Two different crystal forms were obtained by using the vapor diffusion method with 5% isopropanol as the precipitating agent. Both crystal forms were obtained from solutions containing 30 mM sodium cacodylate buffer (pH 7.0), 15 mM MgCl2, and 2 mM d(CG)2. One solution also contained 10 mM spermine tetrachloride. The crystals grew in the form of hexagonal rods measuring up to 0.5 X 0.5 X 2.0 mm. They were mounted in sealed glass capillaries with a droplet of mother liquor, and three-dimensional data were collected to a resolution of 1.3 A by using a Picker diffractometer, although the data beyo...