The HMG box is an 80 amino acid domain found in a variety of eukaryotic chromosomal proteins and transcription factors. Binding to DNA is associated with recognition of structural distortion or manipulation of DNA structure. All the HMG box domains bind to four-way DNA junctions, which must therefore present some feature that is common to the binding targets of this wide variety of proteins. Since the four-way junction can itself adopt a variety of structures depending upon conditions, it is important to determine in which form it exists in complexes with HMG boxes. We find that a single HMG box domain is bound exclusively to the open square form of the junction and that conditions that stabilize the stacked X structure significantly lower affinity for the HMG box. We suggest that the HMG domain binds to one arm of the junction in the minor groove at the point of strand exchange and we present a model for the structure of the complex.

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a risk factor for psychiatric illness through its disruption by a balanced chromosomal translocation, t(1;11)(q42.1;q14.3), that co-segregates with schizophrenia, bipolar disorder and depression. We previously reported that the translocation reduces DISC1 expression, consistent with a haploinsufficiency disease model. Here we report that, in lymphoblastoid cell lines, the translocation additionally results in the production of abnormal transcripts due to the fusion of DISC1 with a disrupted gene on chromosome 11 (DISC1FP1/Boymaw). These chimeric transcripts encode abnormal proteins, designated CP1, CP60 and CP69, consisting of DISC1 amino acids 1–597 plus 1, 60 or 69 amino acids, respectively. The novel 69 amino acids in CP69 induce increased α-helical content and formation of large stable protein assemblies. The same is predicted for CP60. Both CP60 and CP69 exhibit profoundly altered functional properties within cell lines and neurons. Both are predominantly targeted to mitochondria, where they induce clustering and loss of membrane potential, indicative of severe mitochondrial dysfunction. There is currently no access to neural material from translocation carriers to confirm these findings, but there is no reason to suppose that these chimeric transcripts will not also be expressed in the brain. There is thus potential for the production of abnormal chimeric proteins in the brains of translocation carriers, although at substantially lower levels than for native DISC1. The mechanism by which inheritance of the translocation increases risk of psychiatric illness may therefore involve both DISC1 haploinsufficiency and mitochondrial deficiency due to the effects of abnormal chimeric protein expression.GenBank accession numbers: DISC1FP1 (EU302123), Boymaw (GU134617), der 11 chimeric transcript DISC1FP1 exon 2 to DISC1 exon 9 (JQ650115), der 1 chimeric transcript DISC1 exon 4 to DISC1FP1 exon 4 (JQ650116), der 1 chimeric transcript DISC1 exon 6 to DISC1FP1 exon 3a (JQ650117).

Ligand-induced transcription by nuclear receptors involves the recruitment of p160 coactivators such as steroid receptor coactivator 1 (SRC1), in complex with histone acetyltransferases such as CREB-binding protein (CBP) and p300. Here we describe the solution structure of a complex formed by the SRC1 interaction domain (SID) of CBP and the activation domain (AD1) of SRC1, both of which contain four helical regions (C␣1, C␣2, C␣3, and C␣3 in CBP and S␣1, S␣2, S␣2, and S␣3 in SRC1). A tight four-helix bundle is formed between S␣1, C␣1, C␣2, and C␣3 that is capped by S␣3. In contrast to the structure of the AD1 domain of the related p160 protein ACTR in complex with CBP SID, the sequences forming S␣2 and S␣2 in SRC1 AD1 are not involved in the interface between the two domains but rather serve to position S␣3. Thus, although the CBP SID domain adopts a similar fold in complex with different p160 proteins, the topologies of the AD1 domains are strikingly different, a feature that is likely to contribute to functional specificity of these coactivator complexes.The lysine acetyltransferase CBP 5 interacts with a large number of nuclear proteins, many of which are transcription factors (1, 2). This is achieved through direct or indirect protein-protein interactions that are mediated by distinct structural domains within the CBP protein such as the KIX, CRD, CH1, CH3, bromodomain and SID domains. The protein-binding domains of CBP display partial specificity, having both distinct and overlapping binding partner profiles, which contributes to the phenomena of synergy and cross-talk between transcription factors (1).The recruitment of CBP to target gene promoters/enhancers facilitates acetylation of histone N-terminal tails, leading to chromatin remodeling and enhanced gene expression. This has been demonstrated for nuclear receptors, which activate transcription of their target genes in response to ligand binding (3, 4). Ligand-bound receptors undergo a conformational change that stimulates their interaction with cofactors that contain functional LXXLL motifs, such as the p160 coactivators SRC1, TIF2, and ACTR (5, 6). Studies of steroid-regulated gene promoters have revealed that p160s and HAT proteins are among the first cofactors recruited in response to ligand (7,8). Such temporally ordered recruitment of coactivators to promoters/enhancers is crucial for the sequential chromatin modification and remodeling events preceding transcription (4).The efficacy of nuclear receptor/cofactor interaction is influenced by a number of determinants, including the precise sequence and number of LXXLL motifs, the sequences flanking core motifs, and other distal sequences (9 -11). CBP contains three LXXLL motifs, although they mediate only weak direct interactions with estrogen, androgen, and progesterone receptors (9, 10). Thus, at least in the case of the steroid receptors, efficient recruitment of CBP/p300 and associated factors is achieved indirectly via the p160 proteins (12).A number of studies have shown that recruitment of C...

Background: NDE1 and NDEL1 are neurodevelopmental and mitotic proteins with extended coiled-coil N termini, but unknown C-terminal structure.Results: Recombinant NDE1/NDEL1 form dimers and tetramers in which their C termini interact with their N-terminal domains.Conclusion: NDE1/NDEL1 each adopt a sharply bent back structure.Significance: This explains the existence of two distinct dynein-binding domains on NDE1/NDEL1 and instability of disease-associated mutants lacking C termini.