Final answer:
The correct answer to the student's question is CREB, which is a transcription factor that, when phosphorylated by PKA, binds to cis-acting DNA sequences called cAMP Response Elements to regulate gene transcription.
Step-by-step explanation:
The student's question is regarding the cis-acting DNA sequence that binds to the phosphorylated form of a transcription factor regulated by PKA. The correct transcription factor that binds to these cis-acting elements when phosphorylated by PKA is CREB. Other options like β-catenin, C-Jun, and TCF are also transcription factors but they are not the correct answer in the context of this question which pertains to PKA regulation.
CREB stands for cAMP Response Element-Binding protein, and when it is phosphorylated by PKA, it can bind to cAMP Response Elements (CRE), which are specific DNA sequences that regulate the transcription of nearby genes. This mechanism is essential for the regulation of genes that are involved in various cellular processes, such as the increase in cellular metabolism.