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Histidine operon leader peptide
Histidine operon leader peptide (HisL): 16-amino-acid bacterial leader peptide with seven consecutive histidine codons that senses charged tRNA^His in attenuation control of the his biosynthesis operon in E. coli and Salmonella.
Histone acetylation and deacetylation
Histone acetylation and deacetylation: opposing lysine modifications of histones by HATs (acetyl-CoA-dependent) and HDACs (Zn2+- or NAD+-dependent sirtuins) that regulate chromatin and gene expression; also HDAC inhibitor drugs like vorinostat.
Histone deacetylase
Histone deacetylases (HDACs), also called lysine deacetylases, are 18 human enzymes in four classes (zinc-dependent classes I, II, IV; NAD+-dependent sirtuins, class III) that remove acetyl groups from histone and nonhistone proteins; their inhibitors, such as vorinostat and romidepsin, are approved anticancer drugs.
Histone deacetylase inhibitor
Histone deacetylase (HDAC) inhibitors are epigenetic drugs that block zinc-dependent HDAC enzymes, increasing histone acetylation; four (vorinostat, belinostat, romidepsin, panobinostat) are FDA-approved mainly for lymphoma and myeloma.
Histone methylation
Histone methylation: addition of methyl groups to histone lysine or arginine residues, a reversible epigenetic mark written by KMTs/PRMTs, erased by demethylases, and read by methyl-lysine-binding domains; H3K4/H3K36/H3K79 mark active transcription, H3K9/H3K27/H4K20 repression; EZH2 inhibitors tazemetostat and valemetostat are approved cancer drugs.
Histone mRNA 3′ end processing
Histone mRNA 3′ end processing is the pathway that gives replication-dependent histone mRNAs their stem-loop 3′ ends through a single cut directed by the U7 snRNP, with no poly(A) tail added.
HNRP A1 (HNRNPA1)
hnRNP A1 (HNRNPA1), an abundant RNA-binding protein at 12q13.13 with two RRMs, RGG box, and M9 shuttling domain; regulates splicing, telomerase, stress granules, IRES translation; ALS/MSP mutations.
Hok/sok system
Hok/sok is a type I toxin-antitoxin system on E. coli plasmid R1: the Sok antisense RNA represses the pore-forming Hok toxin mRNA, killing plasmid-free daughter cells and stabilizing the plasmid.
Homeobox
Homeobox: a 180-nucleotide DNA sequence encoding the 60-amino-acid homeodomain, a helix-turn-helix DNA-binding motif in developmental transcription factors such as Hox genes, first discovered in Drosophila in 1983.
Homeobox protein
Homeobox protein: transcription factor encoded by a homeobox gene, containing a ~60-amino-acid homeodomain DNA-binding domain. Includes Hox proteins patterning animal body axes; discovered 1984 in Drosophila; distinct from homeobox genes generally.
Homeodomain
Homeodomain: a conserved 60-amino-acid helix-turn-helix DNA-binding domain encoded by the ~180-bp homeobox, discovered in Drosophila in 1984; found in transcription factors across eukaryotes, central to development and disease.
HOTAIR
HOTAIR (HOX transcript antisense intergenic RNA) is a long non-coding RNA from the HOXC cluster that recruits PRC2 and LSD1 to repress HOXD genes in trans; its mouse knockout phenotype and PRC2 role are contested.
Hox gene
Hox genes: clustered homeobox transcription factor genes defining anterior-posterior body patterning in animals; discovered in Drosophila by Ed Lewis, 39 human HOX genes in four clusters, conserved collinearity, roles in development, cancer, and AML.
Hsp90 buffering of genetic variation
Hsp90 buffering of genetic variation is the ability of the Hsp90 chaperone to hide the effects of genetic variants until stress or inhibition reveals them, making Hsp90 a capacitor of variation.
HTH-type transcriptional regulator DicA, C-terminal region
HTH-type transcriptional regulator DicA, C-terminal region: the C-terminal region of DicA, a predicted helix-turn-helix (HTH) DNA-binding transcriptional regulator; class-level features of HTH regulators and related phage repressor domain organization.
I-CreI
I-CreI is a LAGLIDADG homing endonuclease from Chlamydomonas reinhardtii chloroplast 23S rRNA intron; a homodimer cutting a 22-bp pseudo-palindromic site with three metal ions, widely engineered for genome editing.
iCLIP
iCLIP is a molecular biology method that maps where an RNA-binding protein contacts RNA inside cells, using UV crosslinking and sequencing to resolve each crosslink site to a single nucleotide.
IGF2BP1
IGF2BP1, also called IMP1, CRD-BP, or ZBP1, is a human oncofetal RNA-binding protein and class III m6A reader on chromosome 17q21.32 that stabilizes target mRNAs such as MYC and promotes cancer progression and chemoresistance.
IlvB leader peptide
IlvB leader peptide (IvbL, gene ivbL, b3672) is the 32-amino-acid attenuation leader peptide of the E. coli ilvBN operon, rich in valine and leucine codons, controlling branched-chain amino acid biosynthesis.
IlvGEDA operon leader peptide
IlvL, the ilvGEDA operon leader peptide, is a 32-residue branched-chain-amino-acid-rich peptide in enteric bacteria whose translation controls attenuation of the isoleucine-valine biosynthesis operon.
Immediate early response
Immediate early response (IER): rapid cellular gene-expression program in which immediate-early genes (c-fos, c-jun, Egr-1, Arc, IER3) are transcribed within minutes of stimulation without new protein synthesis, via ERK/MAPK signaling.
Immediate-Early Genes
Immediate-early genes (IEGs, primary response genes) are genes expressed rapidly and transiently without new protein synthesis, first named for viral genes; cellular examples include FOS, JUN, EGR1/Zif268, and Arc, central to memory and used as neuronal activity markers.
Imprinting control region
An imprinting control region (ICR) is a cis-acting genetic regulatory element and DNA methylation mark established during gamete formation, which regulates parent-of-origin specific gene expression.
Initiation factor
Initiation factors (IF1, IF2, IF3 in bacteria; eIFs in eukaryotes) are proteins that help ribosomes start translation, position initiator tRNA, and select the start codon; bacteria use three, archaea at least six, eukaryotes at least 12.
Initiator tRNA (tRNA^fMet)
Initiator tRNA is the specialized methionine-carrying transfer RNA that starts protein synthesis, carrying N-formylmethionine in bacteria and organelles, unformylated methionine in eukaryotic and archaeal cytoplasm, and binding directly to the ribosomal P site.
Insulator (genetics)
In genetics, an insulator is a DNA boundary element that blocks enhancer-promoter communication and heterochromatin spread, demarcates chromatin domains, and in mammals depends mainly on the protein CTCF.
Internal transcribed spacer
The internal transcribed spacer (ITS), or ITS sequence, is a non-coding ribosomal DNA region between rRNA genes that serves as the universal DNA barcode for identifying fungi.
Invasion protein InvF
InvF (invasion protein InvF) is an AraC/XylS-family transcriptional activator in Salmonella pathogenicity island 1; with the chaperone SicA it activates effector genes of the SPI-1 type III secretion system and is required for host-cell entry.
Iron-responsive element-binding protein
Iron-responsive element-binding proteins (IRP1/ACO1 and IRP2/IREB2) are cytosolic RNA-binding proteins that bind IRE stem-loops in target mRNAs, post-transcriptionally regulating ferritin, transferrin receptor, and other iron metabolism genes in mammals.
Isoform sequencing
Isoform sequencing (ISO-seq) is a long-read sequencing method that reads full-length RNA transcripts, from the poly(A) tail to the end, identifying complete splice isoforms without assembly.