The lac repressor keeps the production of lactose-digesting enzymes turned off. When allolactose is present, the lac repressor is inactivated, allowing the expression of lactose-digesting enzymes.
DNA methylation, involving the attachment of methyl groups to certain bases, is a mechanism for the long-term inactivation of genes during development.
Testosterone stimulates the expression of genes involved in male sexual characteristics; it follows that the proteins that it interacts with and which bind to DNA will promote transcription.
miRNAs can effectively “silence” genes by binding to mRNA transcripts. The mRNAs are either broken down by enzymes or are unable to physically interact with the ribosomes to complete translation.
They are often capable of changing some fully differentiated cells of different types into their particular cell type.
They may produce proteins that stimulate production of more of the master regulatory gene.
The transcription factors they produce coordinately control related genes.
Many proteins are found concentrated at one end of the cell or another and provide positional information to the developing embryo.
Cell differentiation results from changes in gene expression.
Excess copies of the proto-oncogene could stimulate cell division abnormally, and the inactivation of a tumor-suppressor gene would eliminate a brake on cell division.
Proto-oncogenes can become oncogenes when a mutation or other genetic change increases the activity of the encoded protein.