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RNA Nucleases:

As mentioned before, RNA, unlike DNA, does not last forever because its messages would be created repeatedly. This is unwanted because RNA would endlessly transcribe DNA into a deadly abundance of proteins.To solve this problem, we have enzymes that catalyze RNA hydrolysis: RNA nucleases. These enzymes speed up the process of RNA degradation.

As shown in the mechanism, 2 Histidines and water are needed. The neutral histidine activates the 2’ hydroxyl to attack the phosphate. The positively charged histidine enables the other hydroxyl to be a good leaving group.  Are you wondering why exactly we use histidine? Well, in order for this mechanism to perform successfully, you need an amino acid that is neutral. A neutral characteristic allows it to function as an acid and a base. An amino acid with stronger or weaker acid/base quality is less effective in activating the hydroxyls. With a pka of 7 (pka describes molecule), Histidine is the perfect candidate for a RNA nuclease.

In addition to preventing persistence of message, RNA nucleases serve two other purposes. Like DNA nucleases, they break down exogenous RNA and recycle RNA from cells that have died.

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