Biomedical subjects

Alexander Brechalov

Publications and source records attributed to Alexander Brechalov.

3 recordsLinked to original sources

PubMed2026

An expanded codebook of human transcription factor DNA-binding specificity.

Gene expression is regulated by transcription factors (TFs), which recognize specific DNA sequence motifs. Several hundred putative human TFs, identified mainly by an apparent DNA-binding domain, lack known binding motifs1. Furthermore, even for well-characterized TFs, it remains controversial the degree to which motifs accurately reflect binding sites in living cells2. Here we describe a systematic effort ('Codebook') to determine the sequence specificity of 332 putative and poorly characterized human TFs. More than 4,000 independent experiments, encompassing multiple in vitro and in vivo assays, produced motifs for just over half (177; 53%) of the TFs, of which most are associated with only a single protein. These results extend the vocabulary of sequence recognition encoded by human TFs by around 130 distinct motifs. Moreover, binding motifs identified in vitro are strongly enriched in cellular binding sites. Collectively, the data reveal tens of thousands of previously unknown, conserved and direct TF-binding sites across the human genome. These sites are concentrated in promoter regions and are predictive of gene expression. In summary, this new codebook provides an important step forward in decoding the human genome.

Humans↗

PubMed2026

GHT-SELEX demonstrates unexpectedly high intrinsic sequence specificity and complex DNA binding of many human transcription factors.

There is ongoing debate regarding the degree to which transcription factors (TFs) independently specify genomic binding: TF binding motifs are typically short and degenerate, yielding many more binding site predictions than observed in cells. Here we present genomic high-throughput SELEX (GHT-SELEX)-a scalable method that surveys intrinsic binding of purified TFs to the fragmented, naked and unmodified genome. GHT-SELEX peaks for 179 diverse human TFs display surprisingly high overlap with chromatin immunoprecipitation sequencing peaks for the same TF. Comparable overlap can be obtained from motifs using appropriate analytical approaches. For C2H2 zinc finger (zf) proteins-the largest class of human TFs-GHT-SELEX shows that modular, alternative engagement of C2H2-zf domains is the norm, enabling several types of distinct target sites, and frequently involving internal duplication and divergence within the C2H2-zf array. Altogether, it is common for TFs to delineate a large fraction of in vivo genomic binding sites independently of other cellular factors.

Humans↗

PubMed2024

GHT-SELEX demonstrates unexpectedly high intrinsic sequence specificity and complex DNA binding of many human transcription factors.

A long-standing challenge in human regulatory genomics is that transcription factor (TF) DNA-binding motifs are short and degenerate, while the genome is large. Motif scans therefore produce many false-positive binding site predictions. By surveying 179 TFs across 25 families using >1,500 cyclic in vitro selection experiments with fragmented, naked, and unmodified genomic DNA - a method we term GHT-SELEX (Genomic HT-SELEX) - we find that many human TFs possess much higher sequence specificity than anticipated. Moreover, genomic binding regions from GHT-SELEX are often surprisingly similar to those obtained in vivo (i.e. ChIP-seq peaks). We find that comparable specificity can also be obtained from motif scans, but performance is highly dependent on derivation and use of the motifs, including accounting for multiple local matches in the scans. We also observe alternative engagement of multiple DNA-binding domains within the same protein: long C2H2 zinc finger proteins often utilize modular DNA recognition, engaging different subsets of their DNA binding domain (DBD) arrays to recognize multiple types of distinct target sites, frequently evolving via internal duplication and divergence of one or more DBDs. Thus, contrary to conventional wisdom, it is common for TFs to possess sufficient intrinsic specificity to independently delineate cellular targets.

C2H2↗