Top: The gene is essentially turned off. There is no lactose to inhibit the repressor, so the repressor binds to the operator, which obstructs the RNA polymerase from binding to the promoter and making lactase.
Bottom: The gene is turned on. Lactose is inhibiting the repressor, allowing the RNA polymerase to bind with the promoter, and express the genes, which synthesize lactase. Eventually, the lactase will digest all of the lactose, until there is none to bind to the repressor. The repressor will then bind to the operator, stopping the manufacture of lactase.
Transcription factor
전사인자(轉寫因子, transcription factor)는 진핵생물에서 전사 과정에 참여하는 단백질
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence.[1][2] The function of TFs is to regulate—turn on and off—genes in order to make sure that they are expressed in the right cell at the right time and in the right amount throughout the life of the cell and the organism. Groups of TFs function in a coordinated fashion to direct cell division, cell growth, and cell death throughout life; cell migration and organization (body plan) during embryonic development; and intermittently in response to signals from outside the cell, such as a hormone. There are up to 1600 TFs in the human genome.
TFs work alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase (the enzyme that performs the transcription of genetic information from DNA to RNA) to specific genes.
A defining feature of TFs is that they contain at least one DNA-binding domain (DBD), which attaches to a specific sequence of DNA adjacent to the genes that they regulate.[7][8] TFs are grouped into classes based on their DBDs.[9][10] Other proteins such as coactivators, chromatin remodelers, histone acetyltransferases, histone deacetylases, kinases, and methylases are also essential to gene regulation, but lack DNA-binding domains, and therefore are not TFs. TFs are of interest in medicine because TF mutations can cause specific diseases, and medications can be potentially targeted toward them.
gene expression – the process by which information from a gene is used in the synthesis of a functional gene product such as a protein
Initiation factors can interact with repressors to slow down or prevent translation. They have the ability to interact with activators to help them start or increase the rate of translation. In bacteria, they are simply called IFs (i.e.., IF1, IF2, & IF3) and in eukaryotes they are known as eIFs (i.e.., eIF1, eIF2, eIF3).[1] Translation initiation is sometimes described as three step process by which initiation factors help to carry out. First, the tRNA carrying a methionine amino acid binds to the small ribosome, then binds to the mRNA, and finally joining together with the large ribosome. The initiation factors that help with this process each have different roles and structures.
In cancer
In cancerous cells, initiation factors assist in cellular transformation and development of tumors.The survival and growth of cancer is directly related to the modification of initiation factors and is used as a target for pharmaceuticals. Cells need increased energy when cancerous and derive this energy from proteins. Over-expression of initiation factors correlates with cancers, as they increase protein synthesis for proteins needed in cancers.
Some initiation factors, such as eIF4E, are important in synthesizing specific proteins needed for the proliferation and survival of cancer.[9] The careful selection of proteins ensures that proteins that are usually limited in translation and only proteins needed for cancer cell growth will be synthesized. This includes proteins involved in growth, malignancy, and angiogenesis.[7] The eIF4E factor, along with eIF4A and eIF4G, also play a role in transitioning benign cancer cells to metastatic.
The largest initiation factor, eIF3, is another significant initiation factor in human cancers. Due to its role in creating the 43S pre-initiation complex, it helps to bind the ribosomal subunit to the mRNA. The initiation factor has been linked to cancers through over-expression. For example, one of the thirteen eIF3 proteins, eIF3c, interacts with and represses proteins used in tumor suppression. Limited expression of certain eIF3 proteins, such as eIF3a an eIF3d, has been proven to decrease the vigorous growth of cancer cells.[9] The over-expression of eIF3a has been linked to breast, lung, cervix, esophagus, stomach, and colon cancers. It is prevalent during early stages of oncogenesis and likely selectively translates proteins needed for cell proliferation.[7] When eIF3a is suppressed, it has shown to decrease the malignancy of breast and lung cancer, most likely due to its role in tumor growth.[9]