PolypyrimidinTrakt

PolypyrimidinTrakt is a term used in molecular biology to describe the polypyrimidine tract, a region within pre-mRNA introns that is rich in pyrimidine nucleotides, primarily cytosine and uracil. This tract is typically located upstream of the 3' splice site and plays a key role in the recognition of splice junctions during the early stages of spliceosome assembly.

Function and mechanism

The polypyrimidine tract serves as a binding platform for splicing factors, most notably the U2 auxiliary factor (U2AF) subunit U2AF65, which helps recruit the U2 small nuclear ribonucleoprotein particle to the branch point. The tract also interacts with other RNA-binding proteins, such as polypyrimidine tract-binding protein (PTBP1), which can modulate exon inclusion or skipping. The length and composition of the tract influence splice site strength and the efficiency of intron excision, thereby affecting alternative splicing patterns.

Variation and significance

PolypyrimidinTrakt characteristics vary among introns and species. Longer or more pyrimidine-rich tracts generally enhance 3' splice site recognition, while shorter or disrupted tracts can lead to weaker splicing signals and altered isoform output. Abnormalities in tract length or sequence context have been associated with mis-splicing events implicated in various diseases.

Detection and study

Researchers identify polypyrimidinTrakte through sequence analysis and comparative genomics, often supplemented by experimental assays such as minigene splicing experiments or RNA-seq to observe splicing outcomes. The concept is central to understanding intron–exon architecture and post-transcriptional regulation in eukaryotes.