Author Correction: A massive core for a cluster of galaxies at a redshift of 4.3.

Change history: In this Letter, the Acknowledgements section should have included the following sentence: "The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.". This omission has been corrected online.

A massive core for a cluster of galaxies at a redshift of 4.3.

Massive galaxy clusters have been found that date to times as early as three billion years after the Big Bang, containing stars that formed at even earlier epochs1-3. The high-redshift progenitors of these galaxy clusters-termed 'protoclusters'-can be identified in cosmological simulations that have the highest overdensities (greater-than-average densities) of dark matter4-6. Protoclusters are expected to contain extremely massive galaxies that can be observed as luminous starbursts 7 . However, recent detections of possible protoclusters hosting such starbursts8-11 do not support the kind of rapid cluster-core formation expected from simulations 12 : the structures observed contain only a handful of starbursting galaxies spread throughout a broad region, with poor evidence for eventual collapse into a protocluster. Here we report observations of carbon monoxide and ionized carbon emission from the source SPT2349-56. We find that this source consists of at least 14 gas-rich galaxies, all lying at redshifts of 4.31. We demonstrate that each of these galaxies is forming stars between 50 and 1,000 times more quickly than our own Milky Way, and that all are located within a projected region that is only around 130 kiloparsecs in diameter. This galaxy surface density is more than ten times the average blank-field value (integrated over all redshifts), and more than 1,000 times the average field volume density. The velocity dispersion (approximately 410 kilometres per second) of these galaxies and the enormous gas and star-formation densities suggest that this system represents the core of a cluster of galaxies that was already at an advanced stage of formation when the Universe was only 1.4 billion years old. A comparison with other known protoclusters at high redshifts shows that SPT2349-56 could be building one of the most massive structures in the Universe today.

Cytotoxic activities of Mannich bases of chalcones and related compounds.

Various Mannich bases of chalcones and related compounds displayed significant cytotoxicity toward murine P388 and L1210 leukemia cells as well as a number of human tumor cell lines. The most promising lead molecule was 21 that had the highest activity toward L1210 and human tumor cells. In addition, 21 exerted preferential toxicity to human tumor lines compared to transformed human T-lymphocytes. Other compounds of interest were 38, with a huge differential in cytotoxicity between P388 and L1210 cells, and 42, with a high therapeutic index when cytotoxicity to P388 cells and Molt 4/C8 T-lymphocytes were compared. In general, the Mannich bases were more cytotoxic than the corresponding chalcones toward L1210 but not P388 cells. A ClusCor analysis of the data obtained from the in vitro human tumor screen revealed that the mode of action of certain groups of compounds was similar. For some groups of compounds, cytotoxicity was correlated with the sigma, pi, or molar refractivity constants in the aryl ring attached to the olefinic group. In addition, the IC50 values in all three screens correlated with the redox potentials of a number of Mannich bases. X-ray crystallography and molecular modeling of representative compounds revealed various structural features which were considered to contribute to cytotoxicity. While a representative compound 15 was stable and unreactive toward glutathione (GSH) in buffer, the Mannich bases 15, 18, and 21 reacted with GSH in the presence of the pi isozyme of glutathione S-transferase, suggesting that thiol alkylation may be one mechanism by which cytotoxicity was exerted in vitro. Representative compounds were shown to be nonmutagenic in an intrachromosomal recombination assay in yeast, devoid of antimicrobial properties and possessing anticonvulsant and neurotoxic properties. Thus Mannich bases of chalcones represent a new group of cytotoxic agents of which 21 in particular serves as an useful prototypic molecule.

Bioassembly of acyl lipids in microspore-derived embryos of Brassica campestris L.

The native lipid composition and the capacity of cell-free extracts to biosynthesize acyl lipids in vitro were determined for the first time using the recently reported microspore-derived (MD) embryo system from the Brassica campestris low erucic acid line BC-2 (Baillie et al. 1992). The total lipid fraction isolated from midcotyledonary stage MD embryos (21 days in culture) was composed primarily of triacylglycerol (76%) with an acyl composition quite similar to that of mature BC-2 seed. When incubated in the presence of glycerol-3-phosphate, (14)C 18∶1-CoA, and reducing equivalents, homogenates prepared from 21-day cultured MD embryos were able to biosynthesize glycerolipids via the Kennedy pathway. The maximum in vitro rate of triacylglycerol biosynthesis could more than account for the known rate of lipid accumulation in vivo. The homogenate catalyzed the desaturation of 18∶1 to 18∶2 and to a lesser extent, 18∶3. The newly-synthesized polyunsaturated fatty acids initially accumulated in the polar lipid fraction (primarily phosphatidic acid and phosphatidylcholine) but began to appear in the triacylglycerol fraction after longer incubation periods. As expected for a low erucic acid cultivar, homogenates of MD embryos from the BC-2 line were incapable of biosynthesizing very long chain monounsaturated fatty acyl moieties (20∶1 and 22∶1) from 18∶1-CoA in vitro. Nonetheless, embryo extracts were still capable of incorporating these fatty acyl moieties into triacylglycerols when supplied with (14)C 20∶1-CoA or (14)C 22∶1-CoA. Collectively, the data suggest that developing BC-2 MD embryos constitute an excellent experimental system for studying pathways for glycerolipid bioassembly and the manipulation of this process in B. campestris.

Casein-induced murine amyloidosis: amyloid and immunoglobulin production and proliferative capacity of splenocytes.

We have examined some aspects of lymphocyte and macrophage function in experimental murine amyloidosis. Casein-induced murine amyloidosis is a good model for studying secondary human amyloidosis while myeloma-associated murine amyloidosis is a poor model for human myeloma-associated amyloidosis. The amyloid of casein-induced and myeloma-associated murine amyloidosis cross-reacted immunologically. Neither form of amyloidosis was associated with L chain fragments or excess L chain production. Cellular immunologic reactivity of casein-induced amyloidotic mice, as assessed by lymphocyte transformation with mitogens, was abnormal using spleen lymphocytes but completely normal when thymus and peripheral blood lymphocytes were examined. The depressed activity could be attributed to splenic amyloid deposits. Intracellular amyloid was detected in the spleens of casein-injected mice prior to extracellular amyloid deposits. Amyloid containing cells could also be cultured from the spleen in a much higher proportion than that found in vivo. These cells may represent a subpopulation committed to amyloid synthesis.

Experimental murine amyloidosis: a model system for studying amyloid formation.

Myeloma-associated and casein-induced murine amyloidosis were used as models to study the role of lymphocytes and macrophages in amyloid formation. Amyloidosis occurred rarely and in small amounts in Balb/C mice with immunoglobulin (Ig)-producing myeloma tumours but large amounts could be induced by injections of casein. Fluorescent staining of both forms of amyloid deposits by means of anti-casein- and anti-myeloma-amyloid antibodies indicated that they either crossreacted or coexisted. Nor abnormality of Ig biosynthesis was detected in amyloidosis, suggesting that abnormal degradation was responsible for production of the Ig form of amyloid. Although spleen lymphocytes of casein-injected mice with amyloidosis demonstrated diminished cellular immunologic responses, this did not indicate generalized immunologic incompetence. The non-Ig form of amyloid in casein-injected mice was shown to be produced by macrophages, and a technique was developed for increasing the yield of amyloid-containing cells.