Activation of Notch signaling pathway leads to nuclear translocation of Notch intracellular domain (NIC), and transcriptional activation of target genes through the interaction between CSL proteins (RBPSUH or RBPSUHL) and NIC. HES1, HES5, HEY1 and HEY2 are Notch target genes. Mammalian HES/HEY family proteins as well as Drosophila Hairy and Enhancer of split are implicated in the cell fate determination. We have previously identified and characterized human HES2, HES3 and HES5 genes. Here, we identified and characterized human HES-like (HESL), rat Fesl, and rainbow trout fesl genes by using bioinformatics. Human HESL gene, located within AC093824.3 genome sequence, was mapped to human chromosome 4q35.1 between ACSL1 and SLC25A4 genes. Rat Fesl gene, located within AC111303.4 genome sequence, was mapped to rat chromosome 16q11. EST BX875070.2 was the representative rainbow trout fesl cDNA. HESL-ACSL1 locus was conserved among human, rat, mouse, and zebrafish genomes. Human HESL (241 aa) showed 92.9% total-amino-acid identity with rat Hesl (240 aa), 92.1% total-amino-acid identity with mouse Hesl (240 aa), and 68.0% total-amino-acid identity with rainbow trout hesl (235 aa). HESL orthologs consist of basic Helix-loop-helix (bHLH) domain and ORANGE domain. C-terminal region of HESL orthologs were divergent from that of HES, HEY, and DEC homologs. Phylogenetic analyses revealed that bHLH transcription factors with ORANGE domain were classified into the following three groups: (group I) HES1, HES2, HES4 and HES6 orthologs; (group II) HESL, HES5, HES7, HEY1, HEY2 and HEYL orthologs; (group III) HES3, DEC1/BHLHB2 and DEC2/BHLHB3 orthologs.

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