We have investigated the polymorphism in intron 2 of the interleukin-1 receptor antagonist gene and identified two new alleles of the system. We have shown that the polymorphism is caused by the variable copy number of an 86-bp sequence, by using the polymerase chain reaction and primers immediately flanking the repeat region, and by direct sequencing. The repeat region contains three potential protein-binding sites and therefore the variable copy number may have functional significance.

The ubiquitously expressed mouse Surf-i and Surf-2 genes are divergently transcribed, and their heterogenous start sites are separated by up to a maximum of only 73 bp. By using in vitro DNase I, dimethyl sulfate methylation, and gel retardation assays, we have identified five putative promoter control elements between and around the Surf-i and Surf-2 start sites. The effects of each site on the regulation of Surf-i and Surf-2 transcription have been studied in vivo, and four sites were found to be functional promoter elements. A

Transcription factors of the nuclear factor of activated T cells (NFAT) family play a key role in antigen receptor–mediated responses in lymphocytes by controlling induction of a wide variety of cytokine genes. The GTPases Ras and Rac-1 have essential functions in regulation of NFAT transcriptional activity in the mast cell system, where Fcε receptor type 1 (FcεR1) ligation results in induction of multiple NFAT target genes. This report examines the precise biochemical basis for the Rac-1 dependency of FcεR1 activation of NFAT in mast cells. We are able to place Rac-1 in two positions in the signaling network that regulates the assembly and activation of NFAT transcriptional complexes in lymphocytes. First, we show that activity of Rac-1 is required for FcεR1-mediated NFATC1 dephosphorylation and nuclear import. Regulation of NFAT localization by the FcεR1 is a Rac-dependent but Ras-independent process. This novel signaling role for Rac-1 is distinct from its established regulation of the actin cytoskeleton. Our data also reveal a second GTPase signaling pathway regulating NFAT transcriptional activity, in which Rac-1 mediates a Ras signal. These data illustrate that the GTPase Rac-1 should now be considered as a component of the therapeutically important pathways controlling NFATC1 subcellular localization. They also reveal that GTPases may serve multiple functions in cellular responses to antigen receptor ligation.

Chemical cross‐linking with dithiobis(succinimidyl propionate) has been used to investigate the relative disposition of neighbouring H5 (H1) molecules in chicken erythrocyte chromatin in the extended (nucleosome filament) and condensed (300 A filament) states; in this chromatin H5 and H1 are interspersed along the nucleosome filament, rather than segregated into blocks, as shown by the nature of the cross‐linked dimers and their relative amounts. Detailed analysis of the cross‐linked H5 homopolymers from extended chromatin and condensed nuclear chromatin indicates which domains of H5 are in contact (or close proximity) in the two states. Two results suggest a polar, head‐to‐tail arrangement of H5 molecules along the nucleosome filament. This arrangement persists when chromatin adopts higher‐order structure but in the folded state neighbouring basic C‐terminal domains, in particular, are more closely juxtaposed than they are in extended chromatin.

The organization of the Surfeit locus and the juxtaposition of at least five of the Surfeit genes (Surf-1 to -5) are conserved between mouse and human (Williams et al., 1988; Yon et al., 1993). In the mouse, the heterogeneous transcription start sites of the divergent Surf-1 and Surf-2 genes are separated by a maximum of only 73 bp (Williams and Fried, 1986). This region contains a bidirectional promoter composed of three major factor binding sites required for the efficient expression of both the Surf-1 and Surf-2 genes (Lennard and Fried, 1991). Here we report the isolation and characterization of the human Surf-1 and Surf-2 genes and their intergenic region. Although the major Surf-1 and Surf-2 transcription start sites are separated by 97 bp in the human and there are multiple differences in the mouse and human sequence between and around the transcriptional start sites, there is high conservation of the sequence specifying the three major factor binding sites of the bidirectional promoter. The three factor binding sites (HSu1, 2, and 3) present within the human promoter bind nuclear factors, of which the binding of HSu1 and HSu2 are competed by oligonucleotides carrying the corresponding mouse factor binding sites. The HSu3 site binds factors that are similar but apparently not direct homologs of those that bind to the equivalent mouse sequences. Human Surf-1 and Surf-2 cDNAs have been cloned and sequenced. The putative human Surf-1 and Surf-2 proteins are 77% and 69% identical to the corresponding mouse proteins.