Question

In your opinion, why do you think housekeeping genes have simpler promoter sequences than tissue-specific and dynamically expressed genes?

Answer 1

• The genetic information in the fragment of DNA or a gene, may be expressed by its ability to encode a specific RNA or protein.
• The product thus generated typically “expresses” the genetic information of the gene. As described by the hypothesis of George Wells Beadle and Edward Lawrie Tatum, “One gene one enzyme”; the product of each genetic expression influences the activity of the cell.
• But it is observed that, the cells which contain similar genome, may have completely different functions.
• Hence, this functional variation, in cells having same genome (thus similar genetic code), is attributed to activations and expressions of different genes under different conditions.
• Thus, with same genome, the gene of different cell have the ability, to control and alter their genetic expression. This in turn changes the functional ability of each cell.
• Thus, these genes require more complec promoters with intricate control mechanisms, for gene expression.

• Housekeeping genes express to generate proteins that are essential for the basic functioning of cells or simple functions that are generally required for surviving and functioning.
• Thus, these gene products need to be produced constantly (though may vary at condition like infections) and invariably of the environment.
• Also, the expression of housekeeping genes does not vary with the type of tissues to which they belong, as they have similar basic needs for cellular existence.
• Hence, the promoter of housekeeping genes need not control the type of mRNA generated, with variation of environment, tissues or even organisms.
• Thus, simple promoters are enough for maintaining steady expression of housekeeping genes.