Abstract
Histones are among the most conserved proteins in evolution, sharing a histone fold motif. A number of additional histonic proteins exist and are involved in the process of transcriptional regulation. We describe here the identification, cloning and characterization of two small members of the H2A-H2B sub-family (YBL1 and YCL1) related to the NF-YB and NF-YC subunits of the CCAAT-binding activator NF-Y and to the TATA-binding protein (TBP) binding repressor NC2. Unlike the latters, YBL1 and YCL1 have no intrinsic CCAAT or TATA-binding capacity. In nucleosome reconstitution assays, they can form complexes with histones in solution and on DNA and they are part of relatively large complexes, as determined by glycerol gradient experiments. Our data support the idea that YBL1 and YCL1 are divergent with respect to NF-YB and NF-YC for specific functions, but have coevolved the capacity to interact with nucleosomal structures.
Highlights
Chromatin structure plays a fundamental role in cellular physiology, enabling DNA to be conveniently packed in the relatively small nuclear space
We recently showed that the NF-YB–NF-YC dimer can exist in the absence of NF-YA, that NF-YB and NF-YC can interact with TATA-binding protein (TBP) and that they are partially associated with TFIID; the TBP-contacting parts of NC2β, NF-YC and NF-YB reside in the same short sequence between α3 and αC [15,22]
Because of the relationship with NF-YB–NF-YC, we investigated the possibility that the YBL1–YCL1 dimer could bind to NF-YA and that the resulting trimer might be a CCAATbinding complex
Summary
Chromatin structure plays a fundamental role in cellular physiology, enabling DNA to be conveniently packed in the relatively small nuclear space. Probably the most conserved proteins in evolution, are formed by variable N-terminal tails, subject to several levels of post-translational regulation such as acetylation, phosphorylation, methylation [2] and by the quasi-invariant C-terminal sequences. Analysis of the latter domains revealed a 65 amino acid histone fold motif (HFM). Crystallographic analysis detailing the nucleosomal structure showed that the DDBJ/EMBL/GenBank accession nos AF230805, AF230806 histone fold motif is composed of three α-helices separated by short loops/strand regions, enabling histones to heterodimerize in a compact form and bind DNA in a non-sequence-specific way [4]. Core histones and TAFIIs can interact through their HFMs [10]. (ii) The two subunits α and β of the TBP-binding general repressor NC2
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