Polyadenüleerimine

Polyadenüleerimine is a biological process that occurs in eukaryotic cells. It involves the addition of a string of adenine nucleotides, known as a poly(A) tail, to the 3' end of messenger RNA (mRNA) molecules. This modification is a crucial step in mRNA processing and plays a significant role in gene expression.

The poly(A) tail is not encoded directly in the DNA sequence of a gene. Instead, it is added by an enzyme complex called polyadenylate polymerase after the mRNA transcript has been transcribed from the DNA. This process is coupled with transcription termination and cleavage of the nascent RNA.

The presence of a poly(A) tail confers several important functions to the mRNA molecule. Firstly, it enhances the stability of the mRNA by protecting it from degradation by cellular nucleases. This allows the mRNA to persist in the cytoplasm for a longer duration, enabling more protein to be synthesized from it. Secondly, the poly(A) tail is involved in the export of mRNA from the nucleus to the cytoplasm, where protein synthesis takes place. Finally, it plays a role in the initiation of translation, the process by which the genetic code on the mRNA is used to build proteins. The poly(A) tail interacts with proteins that help recruit ribosomes to the mRNA.

The length of the poly(A) tail can vary, and changes in its length can affect mRNA stability and translation efficiency, thereby influencing gene expression levels. This dynamic regulation of poly(A) tail length is an important mechanism for controlling protein production within the cell.