Final answer:
An increase in gene B transcription is facilitated by the phosphorylation of SRF by PKA, which is activated by cAMP. A situation that raises cAMP levels, such as hormonal stimulation of adenylyl cyclase to convert ATP into cAMP, will lead to this outcome.
Step-by-step explanation:
To determine which situation will lead to an increase in transcription of gene B, it's important to consider the effects of cAMP on Protein Kinase A (PKA), and how this relates to the phosphorylation and activation of transcriptional regulators such as SRF. Increased transcription of gene B occurs when the transcription regulator SRF is phosphorylated by PKA, an event which is dependent on cAMP levels. When cAMP binds to PKA, it triggers a phosphorylation cascade that can result in the activation of transcription factors and gene regulation. An increase in cellular metabolism often results in an upsurge of cAMP, triggering PKA activity, which then translocates to the nucleus. In the nucleus, PKA phosphorylates SRF, leading to increased transcription of gene B. A situation that causes an increase in cAMP would catalyze this process, such as hormonal signaling leading to activation of adenylyl cyclase, the enzyme responsible for converting ATP to cAMP.
Similar to PKA, Protein Kinase C (PKC) also triggers a phosphorylation cascade, which activates transcription factors like NF-KB by inactivating their inhibitors through phosphorylation. However, PKC's activation mechanism is different from PKA's and is not directly related to the cAMP pathway.