Poly A polymerase (PAP) is an enzyme that plays a crucial role in the post-transcriptional modification of RNA molecules. It is responsible for the addition of a polyadenylate (poly A) tail at the 3' end of the messenger RNA (mRNA) molecule. This process, known as polyadenylation, is essential for stability of mRNA and subsequent translation of the genetic information contained within.
Poly A polymerase acts by recognizing a specific sequence on the mRNA called the polyadenylation signal, which is usually located upstream of the cleavage site. Upon recognition, the enzyme cleaves the RNA, leaving an exposed 3' hydroxyl group. It then proceeds to add multiple adenine nucleotides to this exposed end, forming the poly A tail. The length of this tail can vary, typically ranging from 200 to 250 nucleotides in mammals.
The addition of the poly A tail is important for several reasons. Firstly, it protects the mRNA from degradation by exonucleases, enzymes that can rapidly degrade RNA molecules. Secondly, it aids in the export of the mRNA from the nucleus to the cytoplasm, where protein synthesis occurs. Additionally, the poly A tail facilitates the binding of certain proteins called poly(A)-binding proteins, which are involved in the initiation of translation.
In conclusion, poly A polymerase is an enzyme that catalyzes the process of polyadenylation, leading to the addition of a poly A tail at the 3' end of mRNA molecules. This modification is essential for mRNA stability, export, and translation, thereby regulating gene expression.
