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RFE7TN2P–E. coli Holliday junction complex. Molecular model of a RuvA protein (red) in complex with a Holliday junction between homologous strands of DNA (deoxyribonucleic acid, blue) from an E. coli (Escherichia coli) bacterium. A Holliday junction forms during crossing over, a natural genetic process that occurs between homologous chromosomes and leads to the switching of genetic material between the chromosomes. This recombination increases the genetic variation in a population. RuvA is part of the RuvABC complex of three proteins that mediate branch migration and resolve the Holliday junction
RFE7TN42–MHC protein complexed with flu virus. Molecular model showing human class II MHC (major histocompatibility complex) protein HLA-DR1 complexed with an influenza (flu) virus peptide. MHC class II molecules are cell surface molecules that are part of the imm
RFE7TN5H–DNA Holliday junction complex. Molecular model of the enzyme FLP recombinase in complex with a Holliday junction between homologous strands of DNA (deoxyribonucleic acid). A Holliday junction forms during crossing over, a natural genetic process that occu
RFE7TN89–Gene activator protein. Molecular model of catabolite gene activator protein (CAP, yellow) complexed with deoxyribonucleic acid (DNA, red and blue) and RNA polymerase (green and pink). CAP activates genes that enable bacteria to use an alternative energy
RFE7TNJT–EcoRV restriction enzyme. Molecular model of the type II restriction enzyme EcoRV (pink and yellow) bound to a cleaved section of DNA (deoxyribonucleic acid, red and blue). Restriction enzymes, also known as restriction endonucleases, recognise specific n
RFE7TNKM–Reverse transcriptase and inhibitor. Molecular model of HIV reverse transcriptase complexed with a non-nucleoside reverse transcriptase inhibitor drug.
RFE7TNHN–Beta secretase enzyme. Molecular model of the enzyme beta secretase bound to a GGA protein. Beta secretase is a membrane-associated aspartic protease, and is also known as beta-site amyloid precursor protein cleaving enzyme 1 (BACE-1). It is a transmembra
RFE7TN5G–Beta secretase enzyme. Molecular model of the enzyme beta secretase bound to an inhibitor molecule. Beta secretase is a membrane-associated aspartic protease, and is also known as beta-site amyloid precursor protein cleaving enzyme 1 (BACE-1). It is a tra
RFE7TNWY–H5N1 haemagglutinin protein subunit. Molecular model of the haemagglutinin HA(5) subunit. Haemagglutinin is a surface protein from the influenza A virus. Haemagglutinin's function is to bind to the surface of its target cell and allow the viral genes into
RFE7TNHT–Haemagglutinin viral surface protein. Molecular model of haemagglutinin, a surface protein from the influenza virus, complexed with a neutralising antibody. Haemagglutinin's function is to bind to the surface of its target cell and allow the viral genes i
RFE7TN22–Pit-1 transcription factor bound to DNA. Molecular model showing pituitary-specific positive transcription factor 1 (Pit-1) (yellow and pink) bound to a strand of DNA (deoxyribonucleic acid, across centre). Transcription factors are proteins that bind to
RFE7TNJG–RNA interference viral suppressor and RNA. Molecular model of the p19 protein (yellow) from a Tombusvirus, suppressing a double-stranded, small interfering RNA (siRNA) molecule (red and blue). RNA interference, or RNA silencing, has developed in plants as
RFE7TN32–Gene activator protein. Molecular model of catabolite gene activator protein (CAP, pink and green) bound to a molecule of deoxyribonucleic acid (DNA, across top). CAP activates genes that enable bacteria to use an alternative energy source when glucose, t
RFE7TP4B–DNA and MECP2 complex. Molecular model of MECP2 (methyl CpG binding protein 2 (Rett syndrome)) bound to the BDNF (brain-derived neurotrophic factor) gene on a strand of methylated DNA (deoxyribonucleic acid, red and blue). MECP2 is a protein that is essen
RFE7TN6C–Haemoglobin, molecular model. Haemoglobin is a metalloprotein that transports oxygen around the body in red blood cells. Each molecule consists of iron-containing haem groups (sticks) and globin proteins (amino acid chains, coils). Each globin protein is
RFE7TN3T–Human poliovirus particle. Molecular model of the capsid of the human poliovirus. The capsid is a protein coat that encloses the virus's genetic information (genome), stored as RNA (ribonucleic acid). The protruding proteins are receptors, which enable th
RFE7TP4A–DNA and MECP2 complex. Molecular model of MECP2 (methyl CpG binding protein 2 (Rett syndrome)) bound to the BDNF (brain-derived neurotrophic factor) gene on a strand of methylated DNA (deoxyribonucleic acid, red and blue). MECP2 is a protein that is essen
RFE7TNXG–HIV reverse transcription enzyme. Molecular model of the reverse transcriptase enzyme (pink) found in HIV (the human immunodeficiency virus), complexed with a DNA (deoxyribonucleic acid) molecule (green and blue) and the antigen-binding fragment (Fab) of
RFE7TN4G–Oxoguanine glycosylase complex. Computer model showing an 8-Oxoguanine glycosylase (OGG1) molecule (beige) bound to a section of DNA (deoxyribonucleic acid, red and blue). OGG1 is a DNA glycosylase enzyme that is involved in base excision repair - a cellu
RFE7TN3M–DNA Holliday junction. Molecular model of a Holliday junction (centre) between homologous strands of DNA (deoxyribonucleic acid). A Holliday junction forms during crossing over, a natural genetic process that occurs between homologous chromosomes and lead
RFE7TN4Y–Oxoguanine glycosylase complex. Computer model showing an 8-Oxoguanine glycosylase (OGG1) molecule (beige) bound to a section of DNA (deoxyribonucleic acid, red and blue). OGG1 is a DNA glycosylase enzyme that is involved in base excision repair - a cellu
RFE7TN95–Flu virus surface protein and antibody. Molecular model of the neuraminidase glycoprotein enzyme found on the surface of the influenza (flu) virus, in complex with the antigen-binding fragment (Fab) of monoclonal antibody NC41. The presence of neuraminida
RFE7TN4J–LAC repressor bound to DNA. Molecular model of a LAC (lactose) repressor molecule (pink and turquoise) interacting with bacterial DNA (deoxyribonucleic acid, red and blue). The LAC repressor inhibits the expression of genes that code for an enzyme which m
RFE7TNJ6–Haemagglutinin protein subunit. Molecular model of the ectodomain of the haemagglutinin HA(2) subunit. Haemagglutinin is a surface protein from the influenza A virus. Haemagglutinin's function is to bind to the surface of its target cell and allow the vir
RFE7TNX8–RNA-editing enzyme. Molecular model of a left-handed, RNA double helix (Z-RNA, centre) bound by the Z alpha domain of the human RNA-editing enzyme ADAR1 (double-stranded RNA adenosine deaminase, green and gold). ADAR1 de-stabilises double stranded RNA (ri
RFE7TNJB–Transcription factor and DNA molecule. Molecular model of glucocorticoid receptor (GR) transcription factor protein (pink and blue) complexed with a molecule of DNA (deoxyribonucleic acid, red and blue). Transcription factors regulate the transcription of
RFE7TNHW–Foot-and-mouth disease virus. Molecular model of the foot-and-mouth disease (FMD) virus Aphtae epizooticae, with antibodies (immunoglobulins, yellow) attached to the virus's outer protein coat (capsid). FMD affects cloven-hooved mammals, commonly cattle a
RFE7TNN4–Foot-and-mouth disease virus. Molecular model of the foot-and-mouth disease (FMD) virus (Aphtae epizooticae) protein coat (capsid). FMD affects cloven-hooved mammals, commonly cattle and pigs, and is highly contagious. Antibodies are created by an animal'
RFE7TN7X–Enzyme catalysing DNA recombination. Molecular model of the enzyme CRE (cyclization recombination) recombinase (green and purple) mediating the recombination of strands of DNA (deoxyribonucleic acid, red and blue) at a Holliday Junction. This recombinatio
RFE7TP09–MscS ion channel protein structure. Molecular model of a mechanosensitive channel of small conductance (MscS) from an Escherichia coli bacterium. MscSs play a critical role in converting physical stress at the cell membrane into an electrochemical respons
RFE7TN7W–Enzyme catalysing DNA recombination. Molecular model of the enzyme CRE (cyclization recombination) recombinase (green and purple) mediating the recombination of strands of DNA (deoxyribonucleic acid, red and blue) at a Holliday Junction. This recombinatio
RFE7TNY9–MscS ion channel protein structure. Molecular model of a mechanosensitive channel of small conductance (MscS) from an Escherichia coli bacterium. MscSs play a critical role in converting physical stress at the cell membrane into an electrochemical respons
RFE7TNM9–TATA box-binding protein complex. Molecular model showing a yeast TATA box-binding protein (TBP) complexed with a strand of DNA (deoxyribonucleic acid, red and blue) and transcription factor IIB. TBP is a general transcription factor that binds specifical
RFE7TNMX–TATA box-binding protein complex. Molecular model showing a yeast TATA box-binding protein (TBP) complexed with a strand of DNA (deoxyribonucleic acid, red and blue) and transcription factor IIA. TBP is a general transcription factor that binds specifical
RFE7TNKA–Transcription activation of IFN-beta gene. Molecular model of an enhanceosome containing the transcription factors IRF-3, ATF-2 and c-Jun bound to the interferon-beta (IFN-beta) enhancer on a strand of DNA (deoxyribonucleic acid, red and blue). Activation
RFE7TN9B–Human poliovirus particle. Molecular model of the capsid of the human poliovirus. The capsid is a protein coat that encloses the virus's genetic information (genome), stored as RNA (ribonucleic acid). The protruding proteins are receptors, which enable th
RFE7TNK2–RNA-induced silencing complex (RISC), molecular model. This complex consists of a bacterial argonaute protein bound to a small interfering RNA (siRNA) molecule (red and blue). RISC is the multiprotein complex responsible for the gene silencing process kno
RFE7TPF7–HIV-1 protease and inhibitor. Molecular model of the enzyme HIV-1 protease (pink and blue ribbons) bound to an inhibitor molecule (centre). This enzyme, from HIV (human immunodeficiency virus), cleaves viral polyproteins into functional proteins that are
RFE7TNK8–SV40 virus capsid, molecular model. Simian virus 40 (SV40) is found in monkeys such as Rhesus monkeys and macaques. Potentially tumour-causing, it is used in laboratory research and in vaccines. In viruses, the capsid is the protein shell that encloses th
RFE7TN45–Semliki forest virus capsid, molecular model. This virus, named for the forest in Uganda where it was identified, is spread by the bite of mosquitoes. It can infect both humans and animals. In viruses, the capsid is the protein shell that encloses the gen
RFE7TN79–Photosystem I. Molecular model of the photosystem I complex from the cyanobacterium Synechococcus elongatus. Shown here are beta-carotene, alpha-chlorophyll and reaction centre subunits. Photosystems are protein complexes involved in photosynthesis. They
RFE7TN1H–TATA box-binding protein complex. Molecular model showing a yeast TATA box-binding protein (TBP) complexed with a strand of DNA (deoxyribonucleic acid, red and blue) and transcription factor IIB. TBP is a general transcription factor that binds specifical
RFE7TNMW–TATA box-binding protein and DNA. Molecular model showing a TATA box-binding protein (TBP) complexed with a strand of DNA (deoxyribonucleic acid, red and blue). TATA boxes are found in the promoter region of a gene, the area where transcription is initiat
RFE7TN66–Haemoglobin, molecular model. Haemoglobin is a metalloprotein that transports oxygen around the body in red blood cells. Each molecule consists of iron-containing haem groups (sticks) and globin proteins (amino acid chains, coils). Each globin protein is
RFE7TN4T–Restriction enzyme and DNA. Molecular model showing an EcoRI endonuclease enzyme (purple and green) bound to a DNA (deoxyribonucleic acid) molecule (red and blue). EcoRI is an enzyme isolated from strains of E. coli bacteria. It is part of the restriction
RFE7TNY5–HIV antibody therapy. Molecular model of the interaction of the HIV surface protein gp120 (green) as it interacts with a human white blood cell surface protein (CD4, blue) and the anti-HIV antibody (17B, yellow and orange). HIV (the human immunodeficiency
RFE7TNY7–MscL ion channel protein structure. Molecular model of a mechanosensitive channel of large conductance (MscL) from a Mycobacterium tuberculosis bacterium. MscLs play a critical role in converting physical stress at the cell membrane into an electrochemica
RFE7TN48–ATPase molecule. Molecular model of the central stalk of an ATP synthase (ATPase) molecule from a cow. ATPase is an important enzyme that provides energy for cells through the synthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and
RFE7TNWP–RNA-induced silencing complex (RISC), molecular model. This complex consists of a bacterial argonaute protein (top) bound to a small interfering RNA (siRNA) molecule (red and blue). RISC is the multiprotein complex responsible for the gene silencing proce
RFE7TNJP–HIV reverse transcription enzyme. Molecular model of the reverse transcriptase enzyme (blue and green) found in HIV (the human immunodeficiency virus) complexed with a molecule of DNA (deoxyribonucleic acid, pink). Reverse transcriptase transcribes the si
RFE7TNWM–DNA transcription. Molecular model of the enzyme RNA polymerase II synthesising a mRNA (messenger ribonucleic acid) strand from a DNA (deoxyribonucleic acid) template. Polymerase II recognises a start sign on the DNA strand and then moves along the strand
RFE7TNWR–RNA-induced silencing complex (RISC), molecular model. This complex consists of a bacterial argonaute protein (top right) bound to a small interfering RNA (siRNA) molecule (red and blue). RISC is the multiprotein complex responsible for the gene silencing
RFE7TN53–Cre-Lox recombination. Molecular model of the enzyme CRE (cyclization recombination) recombinase (beige) mediating the recombination of strands of DNA (deoxyribonucleic acid, red and blue). It is doing this at a specific target sequence, called the Lox se
RFE7TNWN–Double-stranded RNA-ribonuclease III. Molecular model of ribonuclease III (RNase III, D44N, pink and green) complexed with a double-stranded RNA (ribonucleic acid) strand (red and blue). This ribonuclease is an example of an endoribonuclease, an enzyme th
RFE7TP53–HIV reverse transcription enzyme. Molecular model of the reverse transcriptase enzyme found in HIV (the human immunodeficiency virus) bound to the inhibitor nevirapine. Reverse transcriptase transcribes the single-stranded RNA (ribonucleic acid) genome of
RFE7TP4Y–HIV DNA and transcription factor. Molecular model of DNA (deoxyribonucleic acid) from HIV-1 (human immunodeficiency virus type 1) complexed with the transcription factor kappa B. Transcription factors are proteins that bind to specific sequences of DNA an
RFE7TNXB–3-hydroxyacyl-CoA dehydrogenase, molecular model. This enzyme is found in human heart tissue, and catalyses a reaction that is part of the beta-oxidation pathway. Its full name is short chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD). SCHAD is part of the
RFE7TN4C–HPV surface protein L1, molecular model. This is a complex made up of the protein L1, found in the capsid (outer protein coat) of the human papilloma virus (HPV). L1 spontaneously forms a complex like this which resembles HPV. These complexes have been us
RFE7TP5B–Transcription repressor protein and DNA, molecular model. The repressor protein (green) is binding to a strand of DNA (deoxyribonucleic acid, pink and purple). It acts by physically blocking access to the DNA, preventing the transcription of the genetic i
RFE7TN9X–ATPase and inhibitor. Computer model of an ATP synthase (ATPase) molecule from a mitochondrion complexed with its inhibitor protein IF1. ATPase is an important enzyme that provides energy for cells through the synthesis of adenosine triphosphate (ATP) fro
RFE7TNX5–Multidrug transporter. Molecular model of the multidrug transporter EmrD from the bacterium Escherichia coli. This protein pumps drugs, including antibiotics, out of the bacterial cell.
RFE7TN84–Green fluorescent protein (GFP), molecular model. The molecule has a cylindrical structure formed from beta sheets (ribbons). GFP is found in the Pacific jellyfish Aequorea victoria. It fluoresces green when blue light is shone on it. GFP is widely used a
RFE7TN5Y–Green fluorescent protein (GFP), molecular model. The molecule has a cylindrical structure formed from beta sheets (ribbons). GFP is found in the Pacific jellyfish Aequorea victoria. It fluoresces green when blue light is shone on it. GFP is widely used a
RFE7TN4P–Green fluorescent protein (GFP), molecular model. The molecule has a cylindrical structure formed from beta sheets (ribbons). GFP is found in the Pacific jellyfish Aequorea victoria. It fluoresces green when blue light is shone on it. GFP is widely used a
RFE7TNYA–Multidrug transporter. Molecular model of the multidrug transporter Sav1866 from the bacterium Escherichia coli. This protein pumps drugs, including antibiotics, out of the bacterial cell.
RFE7TP4M–Fenna-Matthews-Olson complex. Molecular model of the Fenna-Matthews-Olson complex from the green sulphur bacterium Prosthecochloris aestuarii. At the centre of each of the three proteins is a bacteriochlorophyll a molecule.
RFE7TNJ4–Human prion protein, molecular model. Prions are abnormal proteins that cause a group of fatal neurodegenerative diseases including BSE in cows and CJD in humans. Prions do not have a nucleic acid (RNA or DNA) genome for replication. Abnormal infectious p
RFE7TN1P–Nucleosome, molecular model. A nucleosome is a subunit of chromatin, the substance that forms chromosomes. It consists of a short length of DNA (deoxyribonucleic acid, red and blue helix) wrapped around a core of eight histone proteins (centre). Here the
RFE7TP5G–Ebola viral protein 35 and RNA. Molecular model of the Ebola viral protein 35 (VP35) bound to a molecule of double stranded RNA (ribonucleic acid). This protein helps the virus to evade its host's immune system.
RFE7TN1X–Aspartyl-tRNA synthetase protein molecule. Molecular model showing bacterial aspartyl-tRNA synthetase complexed with aspartyl tRNA (transfer ribonucleic acid). Aspartyl-tRNA synthetase attaches the correct amino acid, in this case aspartyl, onto the corre
RFE7TN7E–HIV reverse transcription enzyme. Molecular model of the reverse transcriptase enzyme found in HIV (the human immunodeficiency virus) bound to the inhibitor nevirapine. Reverse transcriptase transcribes the single-stranded RNA (ribonucleic acid) genome of
RFE7TN4H–Artwork of the human erythropoietin (EPO) hormone molecule (yellow) bound to receptors (pink). Erythropoietin regulates blood oxygen levels in the body, when levels are low it is released to stimulate the formation of red blood cells. It is used illegally
RFE7TN6G–HIV reverse transcription enzyme. Molecular model of the reverse transcriptase enzyme found in HIV (the human immunodeficiency virus). Reverse transcriptase transcribes the single-stranded RNA (ribonucleic acid) genome of HIV into DNA that is capable of i
RFE7TP7C–Flock house virus capsid, molecular model. The flock house virus is a member of the Nodaviridae family. It kills the New Zealand grass grub insect.
RFE7TNJ3–Herpesvirus immune inhibitor protein. Molecular model of the protein ICP47 from the herpes simplex virus-1 (HSV-1). This protein prevents antigens from the virus being presented to immune cells, therefore masking it from the immune system. This virus infe
RFE7TP68–Oxidoreductase enzyme complex, molecular model. This is the membrane-bound domain formed from of a complex of NADH-quinone oxidoreductase subunits. The whole is termed respiratory complex I, due to its role in the biochemistry of the cellular respiratory
RFE7TN75–Multidrug efflux pump. Molecular model of the multidrug efflux pump AcrB from the bacterium Escherichia coli. This protein pumps drugs, including antibiotics, out of the bacterial cell.
RFE7TNJA–Androgen receptor. Molecular model of the DNA-binding region of an androgen receptor (pink and yellow) complexed with DNA (deoxyribonucleic acid, blue and red). Androgen receptors are nuclear receptors that are activated by binding of either of the androg
RFE7TNN2–Bacteriophage DNA recombination. Molecular model showing DNA manipulation and recombination taking place at a Holliday junction with a bacteriophage enzyme. DNA is multicoloured, while the lambda-int integrase protein from a lambda bacteriophage is beige.
RFE7TN6K–MHC protein-antigen complex. Molecular model of the human class I MHC (major histocompatibility complex) protein HLA-B27 complexed with beta-2 microglobulin. MHC class I molecules are cell surface molecules that are part of the immune system. They are fou
RFE7TNJ7–Endonuclease IV molecule. Molecular model of the endonuclease IV restriction enzyme EcoRV (beige) bound to a cleaved section of DNA (deoxyribonucleic acid, blue, red and green). Restriction enzymes, also known as restriction endonucleases, recognise speci
RFE7TN5C–Isoleucyl-tRNA synthetase protein molecule. Molecular model showing bacterial isoleucyl-tRNA synthetase complexed with aspartyl tRNA (transfer ribonucleic acid). Isoleucyl-tRNA synthetase attaches the correct amino acid, in this case isoleucyl, onto the c
RFE7TN9Y–Dengue virus surface protein molecule. Molecular model of the envelope glycoprotein found on the surface of the dengue haemorrhagic fever (DHF) virus. The function of this protein is to bind to the surface of its target cell and allow the viral genes into
RFE7TNJY–Parvovirus particle. Molecular model showing the structure of the capsid (outer protein coat) of a human parvovirus (family Parvoviridae) particle. Parvoviridae viruses include the smallest known viruses and some of the most environmentally resistant. Eac
RFE7TNMN–Cholera toxin, molecular model. Cholera toxin is a protein complex secreted by the bacterium Vibrio cholerae, that causes the disease cholera. It is made up of a wedge-shaped A subunit (pink and blue) and five B subunits (across top) that form a ring whic
RFE7TN3Y–Lumazine synthase molecule. Molecular model showing the structure of a lumazine synthase enzyme molecule from a Brucella abortus bacterium. This protein, also known as riboflavin synthase, is found in bacteria, archaea, plants and fungi, where it catalyse
RFE7TP71–Flu virus surface protein and drug. Molecular model of the neuraminidase glycoprotein enzyme from on the surface of the influenza A (flu) virus bound to the drug zanamivir. The function of this protein is to enable the virus to be released from the host c
RFE7TN2K–ATP synthase molecule. Molecular model showing the structure of ATP synthase (ATPase) subunit A and C. ATPase is an important enzyme that provides energy for cells through the synthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and
RFE7TN43–Hepatitis D virus ribozyme complex. Molecular model showing an RNA (ribonucleic acid) strand from an Hepatitis delta (Hepatitis D) virus genomic ribozyme, complexed with a ribonucleoprotein. Ribozymes (ribonucleic acid enzymes) are RNA molecules capable o
RFE7TNMK–RNA stem-loop motif. Molecular model of the stem-loop II motif from the SARS (severe acute respiratory syndrome) coronavirus. This RNA (ribonucleic acid) element is a target for antiviral drugs.
RFE7TN1K–Interleukin-6. Molecular model of the cytokine protein human interleukin-6. This protein is produced in the body and has a wide variety of functions in the immune system.
RFE7TN5X–Valyl-tRNA synthetase protein molecule. Molecular model showing bacterial valyl-tRNA synthetase complexed with valyl tRNA (transfer ribonucleic acid). Valyl-tRNA synthetase attaches the correct amino acid, in this case valyl, onto the corresponding tRNA m
RFE7TN1T–Chaperonin protein complex. Molecular model showing the structure of a GroEL GroES (ADP)7 chaperonin complex. Chaperonins are proteins that provide favourable conditions for the correct folding of other proteins, thus preventing aggregation (clumping) due
RFE7TPF5–Bacterial alpha-hemolysin toxin, molecular model. This toxin is secreted by the bacterium Staphylococcus aureus. It is an example of a pore-forming toxin, forming pores in the membranes of affected cells, damaging or killing them (making it a cytolytic pr
RFE7TP6B–cAMP-dependent protein kinase, molecular model. This enzyme is also known as protein kinase A (PKA). This is the holoenzyme, which consists of two regulatory subunits and two catalytic subunits. Protein kinase enzymes modify other proteins by chemically a
RFE7TN7P–Dengue virus capsid, molecular model. This virus, transmitted by mosquito bites, causes the tropical disease dengue fever in humans. In viruses, the capsid is the protein shell that encloses the genetic material. A capsid consists of subunits called capso
RFE7TNAC–Photosynthetic reaction centre. Molecular model of the photosynthetic reaction centre from the purple bacterium Rhodopseudomonas viridis. This complex contains enzymes that absorb light and use it to reduce (add electrons to) other molecules.
RFE7TNKN–LAC repressor. Molecular model of a LAC (lactose) repressor molecule. The LAC repressor inhibits the expression of genes that code for an enzyme which metabolizes lactose in bacteria. It is only present when lactose levels are low. This ensures that the b
