Transcription Positive regulation

Positive regulators (enhancers) Turn on transcription when a specific effector protein binds to a specific enhancer sequence in the DNA. 

Figure 1 The MAPK pathway and its connections to other signals A negative feedback loop connects the phosphorylated endpoint of the pathway ERK (Extracellular-signal Regulated Kinase) to the transcriptionally-driven synthesis of the phosphatase, MKP MAP kinase phosphatase. MKP then de-phosphorylates ERK to shut down the signaling cascade. The positive feedback loop again starts with the terminal kinase ERK which activates cPLA2 (cytosolic phospholipase A2). This leads to the synthesis of arachidonic acid, which, in turn activates protein kinase C (PKC). PKC is a positive regulator of RAS (Please see Color Plate Section in the back of this book).

These different reports indicate that nucleolin could influence transcription positively or negatively. These seemingly contradictory data might be explained if one considers that nucleolin does not act as a real transcriptional activator or repressor, but rather indirectly through the regulation of chromatin structure. 

Positive regulation implies that the bound protein stimulates transcription. Such proteins are termed transcriptional activators. Transcriptional activation plays a central role in eukaryotes (see 1.4.3). There are various mechanisms of transcriptional activation. 

The transcription of genes for metallothionein is imder positive regulation by the DNA-binding protein ACE, which binds an ACE-specific DNA element in the metal-... 

In this system, cognate hormones act as positive regulating effectors. The transcription regulating activity of nuclear receptors can also be negatively influenced by specific inhibitor proteins. These proteins are characterized as repressors. 

Driever, W. and Nusslein-Volhard, C. The bicoid protein is a positive regulator of hunchback transcription in the early Drosophila embryo (1989) Nature 337,138-143... 

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