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Previous studies have found that, when injected into mice, glycolipidic fractions of mycobacterial cell walls containing phosphatidylinositol mannosides (PIM) induced a granuloma and recruitment of Natural Killer T cells in the lesions. The dimannoside (PIM 2 ) and the hexamannoside (PIM 6 ) PIM were isolated from Mycobacterium bovis bacillus Calmette Gué rin and shown to act alike, but the activity was found to be dependent on the presence of the lipidic part. The chemical structure of PIM was then re-evaluated, focusing on the characterization of their lipidic part, defining mono-to tetraacylated PIM 2 . The structure of these acyl forms was elucidated using a sophisticated combination of chemical degradations and analytical tools including electrospray ionization/mass spectrometry, electrospray ionization/mass spectrometry/mass spectrometry, and twodimensional NMR. Finally, the acyl forms were purified by hydrophobic interaction chromatography and tested for their capacity to induce the granuloma and Natural Killer T cell recruitment. We found that there is an absolute requirement for the molecules to possess at least one fatty acyl chain, but the number, location, and size of the acyl chains was without effect. Moreover, increasing the complexity of the carbohydrate moiety did not lead to significant differences in the biological responses. Phosphatidyl-myo-inositol mannosides (PIM)1,2 constitute a group of phospholipids found in the cell wall and the cytoplasmic membrane of mycobacteria along with cardiolipid, phosphatidylethanolamine, and phosphatidylinositol. Known from the 1940s and fully described by Ballou and colleagues (1) in the 1960s, they were shown to consist of phosphatidyl-myoinositol di-, tri-, tetra-, and pentamannosides (PIM 2 to PIM 5 ). These authors showed unequivocally that in PIM 2 the mannosyl units were glycosidically attached at positions 2 and 6 of the myo-Ins ring (2) and that for the more glycosylated forms, chain elongation occurred on the mannose present at position 6 (3). Recently, PIM from Mycobacterium smegmatis were reanalyzed in their deacylated form (4). They were shown to have a structure based on that defined by Ballou et al.(1) but containing six mannosyl residues (PIM 6 ). The structure of the glycosidic part of PIM 6 is now unambiguously established and corresponds to Manp␣-13(2-Manp␣-1) 2 3(6-Manp␣-1) 2 3 linked to position 6 of the myo-Ins ring beside the mannosyl residue present at position 2. This structure was confirmed by an NMR spectroscopy strategy applied to deacylated PIM 6 (5).Concerning the lipidic part of the PIM, the situation is still unclear, although the presence of multiacylated forms of PIM was already reported in 1960s by several authors (6 -9) working on different mycobacterial strains. More recently, in a chromatographic and fatty acid quantitation study of mycobacterial lipoglycans, Leopold and Fisher (10) also inferred the existence of multiacylated forms of PIM. However, the sites of attachment of the acyl groups were not established. Re-evalu...

We found that c-kit-positive, lineage marker-negative, Thy-1lo cells are present in both bone marrow and thymus ("BM c-kit" and "thymus c-kit" cells). Although the two cell types are phenotypically similar, only BM c-kit cells showed the potential to form colonies in vitro as well as in vivo. However, both of them revealed extensive growth and differentiation potential to T cells after direct transfer into an irradiated adult thymus, or a deoxyguanosine-treated fetal thymus. Time course analysis showed that thymus c-kit cells differentiated into CD4CD8 double-positive cells approximately 4 d earlier than BM c-kit cells did. In addition, anti-c-kit antibody blocked T cell generation of BM c-kit cells but not of thymus c-kit cells. Intravenous injection of thymus c-kit resulted in the generation of not only T cells, but B as well as NK1.1+ cells. These data provide evidence that thymus c-kit cells represent common lymphoid progenitors with the differentiation potential to T, B, and possibly NK cells. The c-kit-mediated signaling appears to be essential in the transition from BM c-kit to thymus c-kit cells.

Biochemistry. In the article "Clonal selection and in vivo quantitation of protein interactions with protein-fragment complementation assays" by Ingrid Remy and Stephen W. Michnick, which appeared in number 10, May 11, 1999, of Proc. Natl. Acad. Sci. USA (96, 5394-5399) Immunology. In the article entitled "Murine natural killer cells contribute to the granulomatous reaction caused by mycobacterial cell walls" by I. Apostolou, Y. Takahama, C. Belmant, T. Kawano, M. Huerre, G. Marchal, J. Cui, M. Taniguchi, H. Nakauchi, J.-J. Fournié, P. Kourilsky, and G. Gachelin, which appeared in number 9, April 27, 1999 of Proc. Natl. Acad. Sci. USA (96,(5141)(5142)(5143)(5144)(5145)(5146), the authors request that the following correction be noted: the title should be "Murine natural killer T (NKT) cells contribute to the granulomatous reaction caused by mycobacterial cell walls." Neurobiology. In the articles "An empirical basis for Mach bands" by R. Beau Lotto, S. Mark Williams, and Dale Purves, which appeared in number 9, April 27, 1999, of Proc. Natl. Acad. Sci. USA (96,(5239)(5240)(5241)(5242)(5243)(5244), and "Mach bands as empirically derived associations" by R. Beau Lotto, S. Mark Williams, and Dale Purves, which appeared in number 9, April 27, 1999, of Proc. Natl. Acad. Sci. USA (96,(5245)(5246)(5247)(5248)(5249)(5250), the following correction should be noted. The reproduction of some of the figures in these papers was unsatisfactory due to the presence of moiré patterns and other deficiencies in the published versions. Given the difficulty in faithfully reproducing gradients in print, readers may wish to view the electronic versions of the figures at purveslab.neuro.duke.edu.Psychology. In the article "Spatial attention affects brain activity in human primary visual cortex" by Sunil P. Gandhi, David J. Heeger, and Geoffrey M. Boynton, which appeared in number 6, March 16, 1999, of Proc. Natl. Acad. Sci. USA (96, 3314-3319), due to an error in the PNAS office, a sentence was omitted. The sentence is shown in bold type in context in the complete paragraph below.On the other hand, it is certainly possible that the V1 modulation we observed might have nothing to do with the improved behavioral performance. For example, the memory load differs between the tasks in the main experiment and the spatial uncertainty experiment. In the spatial uncertainty experiment, subjects must remember two speeds instead of one during the 250 msec inter-stimulus interval. This difference in memory load might be causing the improved behavioral performance. Or the improved performance may result from subjects simply ignoring information from the uncued side, and thus may not be causally related to V1 modulation. It is difficult, however, to imagine that such a significant modulation of activity in visual cortex would fail to have consequences on perceptual thresholds. 7610

Transcription of the c‐jun gene is up‐regulated by either retinoic acid (RA) or adenovirus E1A during the differentiation of F9 cells. We show here that RA and E1A induce phosphorylation of the E1A‐associated 300 kDa protein (p300) during the differentiation of F9 cells. The region of E1A that is required for interaction with cellular protein p300 overlaps with the region of E1A required for E1A to induce expression of the c‐jun gene. Treatment of F9 cells with RA or infection of the cells by adenovirus led to a decrease in the electrophoretic mobility of p300. Phosphatase treatment of p300 from RA‐treated or adenovirus‐infected F9 cells reversed the changes in migration of p300, indicating that RA‐ and E1A‐mediated changes in the mobility of p300 were due to phosphorylation. We also found factors, designated DRF1 and DRF2, that bound specifically to a sequence element that is necessary and sufficient for RA‐ and E1A‐mediated up‐regulation of the c‐jun gene. The mobility of DRF complexes was changed by E1A or RA and the complexes were supershifted by addition of a polyclonal p300 antiserum. Moreover, overexpression of p300 resulted in an increase in the level of DRF1 complex. p300 fused to the DNA binding domain of the E2 protein of papilloma virus stimulated E2‐dependent reporter activity in response to RA or E1A in F9 cells. Our results suggest that p300 is part of the DRF complexes, that it is differentially phosphorylated in undifferentiated versus differentiated cells and that it is likely involved in regulating transcription of the c‐jun gene during F9 cell differentiation.

Differentiation of mouse F9 embryonal carcinoma (EC) cells can be induced by exposure to retinoic acid (RA) or by expression of adenovirus E1A. The transcription of the c‐jun gene is stimulated by either RA or E1A. We report here that both RA and E1A strongly induce the expression of chloramphenicol acetyltransferase (CAT) from c‐jun promoter/CAT reporter construct (c‐jun/CAT), which is stably integrated into F9 cells, in a manner that is independent of both copy number and integration locus. The induction of c‐jun/CAT expression is observed in undifferentiated F9 cells, but not in differentiated F9 cells, adenovirus‐infected F9 cells or HeLa cells. Deletion analysis of the promoter region of the c‐jun gene indicates that the sequence elements required for the RA‐ and E1A‐mediated induction are identical and they have been defined as a region of 145 bp between −190 and −46 of the 5′ flanking region of c‐jun. This RA and E1A response element (RERE) contains five variants of the motif CGCGGTGACGNT. The upstream two motifs are adjacent and extend in opposite directions, creating an imperfect palindrome. The downstream four motifs are located at 35 or 36 bp intervals in the same orientation. Substitution and insertion analysis indicates that these motifs and their regular intervals are important for the activity of the RERE.

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