PAB1

Pab1, short for poly(A)-binding protein 1, is a cytoplasmic RNA-binding protein that binds the polyadenylate tails of messenger RNAs. It is highly conserved among eukaryotes, with the Saccharomyces cerevisiae protein encoded by the PAB1 gene serving as a well-studied model. Pab1 participates in mRNA metabolism, influencing stability, translation, and the regulation of poly(A) tail length.

The protein’s amino-terminal region contains four RNA recognition motif (RRM) domains responsible for high-affinity binding to poly(A) sequences. The C-terminal region includes an MLLE/PABC domain that mediates protein–protein interactions with factors containing MLLE-binding motifs. This modular architecture enables Pab1 to bridge poly(A) tails with other components of the translation machinery.

Functionally, Pab1 stabilizes mRNA by protecting the poly(A) tail from excessive deadenylation and promotes efficient translation initiation. It cooperates with eukaryotic initiation factors, particularly eIF4G, to facilitate the formation of a closed-loop mRNA structure that enhances ribosome recycling and translation efficiency. Pab1 also participates in the regulation of deadenylation, balancing tail shortening with translation-dependent protection.

Localization and dynamics of Pab1 are predominantly cytoplasmic, and it can relocalize to stress granules and processing bodies under cellular stress. The protein is essential for normal mRNA metabolism in yeast, and its functions are broadly conserved across eukaryotes, where the PABP family includes multiple paralogs with specialized or tissue-specific roles.

See also PABP, poly(A) tail, translation initiation, mRNA stability.