Figure 1.

(A) The addition of serum to serum-starved cells leads to the immediate induction of expression of a number of genes. Some of these ‘immediate early response genes’ encode transcription factors such as c-fos and c-jun that turn on ‘late response genes.’ The expression of immediate early genes decreases after an initial rise, but the late response genes are expressed in a sustained manner over time. This figure is derived from Lodish et al (2000). (B) Diagram showing the relationships among members of the c-fos/c-jun pathway that were investigated. Species whose levels were measured in single cells are indicated by gray arrows below the blocks. We measured the heterodimers and downstream mRNAs in the same cells, rather than upstream and downstream mRNAs, because by the time downstream mRNAs begin to get expressed, the c-fos and c-jun mRNAs disappear from the cells.