Cooperative DNA base and shape recognition by the CCAAT-binding complex and its bZIP transcription factor HapX

The heterotrimeric CCAAT-binding complex (CBC) is a master regulator of transcription. It specifically recognizes the CCAAT-box, a fundamental eukaryotic promoter element. Certain fungi, like Aspergilli, encode a fourth CBC-subunit, HapX, to fine-tune expression of genes involved in iron metabolism. Although being a basic region leucine zipper with its own DNA recognition motif, HapX function strictly relies on the CBC. We here report two crystal structures of the CBC-HapX complex bound to DNA duplexes with distinct sequence and position of HapX sites. In either structure, a HapX dimer targets the nucleic acid downstream of the CCAAT-box and the leash like N-terminus of the distal HapX subunit interacts with CBC and DNA. In vitro and in vivo analyses of HapX mutants support the structures, highlight the complex as an exceptional major and minor groove DNA binder, and enrich our understanding of the functional as well as structural plasticity of related complexes across species.

Mathematical Algorithm for Identification of Eukaryotic Promoter Sequences

Identification of promoter sequences in the eukaryotic genome, by computer methods, is an important task of bioinformatics. However, this problem has not been solved since the best algorithms have a false positive probability of 10−3–10−4 per nucleotide. As a result of full genome analysis, there may be more false positives than annotated gene promoters. The probability of a false positive should be reduced to 10−6–10−8 to reduce the number of false positives and increase the reliability of the prediction. The method for multi alignment of the promoter sequences was developed. Then, mathematical methods were developed for calculation of the statistically important classes of the promoter sequences. Five promoter classes, from the rice genome, were created. We developed promoter classes to search for potential promoter sequences in the rice genome with a false positive number less than 10−8 per nucleotide. Five classes of promoter sequences contain 1740, 222, 199, 167 and 130 promoters, respectively. A total of 145,277 potential promoter sequences (PPSs) were identified. Of these, 18,563 are promoters of known genes, 87,233 PPSs intersect with transposable elements, and 37,390 PPSs were found in previously unannotated sequences. The number of false positives for a randomly mixed rice genome is less than 10−8 per nucleotide. The method developed for detecting PPSs was compared with some previously used approaches. The developed mathematical method can be used to search for genes, transposable elements, and transcript start sites in eukaryotic genomes.

Mapping the dynamic transfer functions of epigenome editing

Biological information can be encoded in the dynamics of signaling components which has been implicated in a broad range of physiological processes including stress response, oncogenesis, and stem cell differentiation. To study the complexity of information transfer across the eukaryotic promoter, we screened 119 dynamic conditions—modulating the frequency, intensity, and pulse width of light—regulating the binding of an epigenome editor to a fluorescent reporter. This system revealed highly tunable gene expression and filtering behaviors and provided the most comprehensive quantification to date of the maximum amount of information that can be reliably transferred across a promoter as ∼1.7 bits. Using a library of over 100 orthogonal epigenome editors, we further determined that chromatin state could be used to tune mutual information and expression levels, as well as completely alter the input-output transfer function of the promoter. This system unlocks the information-rich content of eukaryotic epigenome editing.

The UCSC Genome Browser database: 2021 update

For more than two decades, the UCSC Genome Browser database (https://genome.ucsc.edu) has provided high-quality genomics data visualization and genome annotations to the research community. As the field of genomics grows and more data become available, new modes of display are required to accommodate new technologies. New features released this past year include a Hi-C heatmap display, a phased family trio display for VCF files, and various track visualization improvements. Striving to keep data up-to-date, new updates to gene annotations include GENCODE Genes, NCBI RefSeq Genes, and Ensembl Genes. New data tracks added for human and mouse genomes include the ENCODE registry of candidate cis-regulatory elements, promoters from the Eukaryotic Promoter Database, and NCBI RefSeq Select and Matched Annotation from NCBI and EMBL-EBI (MANE). Within weeks of learning about the outbreak of coronavirus, UCSC released a genome browser, with detailed annotation tracks, for the SARS-CoV-2 RNA reference assembly.

EPD in 2020: enhanced data visualization and extension to ncRNA promoters

The Eukaryotic Promoter Database (EPD), available online at https://epd.epfl.ch, provides accurate transcription start site (TSS) information for promoters of 15 model organisms plus corresponding functional genomics data that can be viewed in a genome browser, queried or analyzed via web interfaces, or exported in standard formats (FASTA, BED, CSV) for subsequent analysis with other tools. Recent work has focused on the improvement of the EPD promoter viewers, which use the UCSC Genome Browser as visualization platform. Thousands of high-resolution tracks for CAGE, ChIP-seq and similar data have been generated and organized into public track hubs. Customized, reproducible promoter views, combining EPD-supplied tracks with native UCSC Genome Browser tracks, can be accessed from the organism summary pages or from individual promoter entries. Moreover, thanks to recent improvements and stabilization of ncRNA gene catalogs, we were able to release promoter collections for certain classes of ncRNAs from human and mouse. Furthermore, we developed automatic computational protocols to assign orphan TSS peaks to downstream genes based on paired-end (RAMPAGE) TSS mapping data, which enabled us to add nearly 9000 new entries to the human promoter collection. Since our last article in this journal, EPD was extended to five more model organisms: rhesus monkey, rat, dog, chicken and Plasmodium falciparum.