CRMs are stretches of DNA, usually 100–1000 DNA base pairs in length, where a number of transcription factors can bind and regulate expression of nearby genes and regulate their transcription rates. They are labeled as "cis" because they are typically located on the same DNA strand as the genes they control as opposed to "trans", which refers to effects on genes not located on the same strand or farther away, such as transcription factors. One "cis"-regulatory element can regulate several genes, and conversely, one gene can have several "cis"-regulatory modules. "Cis"-regulatory modules carry out their function by integrating the active transcription factors and the associated co-factors at a specific time and place in the cell where this information is read and an output is given.