Using powerful new sequencing technologies, investigators can now catalog every RNA molecule made by a cell and determine at what quantities these RNAs are present. In an experiment, researchers measured the relative quantities of two different mRNAs—one transcribed from gene A, the other from gene B—in two different cell types. Gene B is expressed in both the liver and the brain whereas gene A is expressed in the brain but not in the liver. Which most likely encodes a housekeeping protein?

Choose one:

A. both genes

B. neither gene

C. gene B only

D. gene A only

Housekeeping proteins are essential for all cells throughout it human body, to maintain basic function. So, if gene B is expressed in two different organs, such as brain and liver, it suggests that B is a housekeeping protein. Examples of this kind of proteins are the ribosomal proteins, RNA polymerases, cytoeskeleton proteins, and some of the mitochondrial proteins, among others.