RNA Sequencing 101: Poly(A) Tail

mRNA Poly(A) Tail

The poly-A tail, a string of adenine nucleotides added to the 3' end of mRNA during post-transcriptional processing, is a defining characteristic of eukaryotic transcripts. This tail serves multiple functions, including mRNA stability, transport, and translation initiation. By protecting mRNA from degradation and facilitating its interaction with ribosomes, the poly-A tail ensures efficient protein production.


Poly(A) tails play several important roles in gene expression. They contribute to mRNA stability, enhance translation efficiency, and are involved in the nuclear export of mature mRNAs. The presence of a poly(A) tail is necessary for efficient transport of the mRNA from the nucleus to the cytoplasm, where it undergoes translation into protein.

Poly(A) Tail Length

The length of poly(A) tails can vary significantly among species and even among different transcripts within the same organism. As you mentioned, the average length of human poly(A) tails is around 250-300 nucleotides (nt). In yeast, the average length is shorter, typically around 70-80 nt. Arabidopsis, a plant species, has an average poly(A) tail length of approximately 51 nt.

Roles of mRNA poly(A) tails in regulation of eukaryotic gene expression.Roles of mRNA poly(A) tails in regulation of eukaryotic gene expression. (Passmore et al., 2022)


The length of the poly(A) tail is dynamically regulated during mRNA metabolism. The addition and removal of adenine nucleotides from the poly(A) tail are controlled by specific enzymes. These enzymes, known as poly(A) polymerases and poly(A)-specific ribonucleases, respectively, play crucial roles in maintaining the appropriate poly(A) tail length for each mRNA.

Transcriptional Regulation

Changes in poly(A) tail length can provide insights into the transcriptional regulation mechanisms of genes. Various stimuli and cellular conditions can lead to alterations in poly(A) tail length, which, in turn, can affect mRNA stability and translation efficiency. Monitoring poly(A) length changes can help researchers understand how gene expression is regulated in response to different signals and during various biological processes.

Why Should We Study Poly(A) Tail in RNA Research?

It related the role of the poly-A tail in mRNA.

mRNA Stability and Degradation

Poly(A) tails play a critical role in mRNA stability. Shortening of the poly(A) tail is often associated with mRNA decay, while lengthening can enhance mRNA stability. By studying poly(A) tail dynamics, researchers can gain insights into the factors and mechanisms involved in mRNA degradation and stability.

mRNA Localization and Transport

Poly(A) tails are involved in the transport of mature mRNA from the nucleus to the cytoplasm. They facilitate the binding of specific proteins that are responsible for mRNA export. Investigating poly(A) tail length and associated proteins can provide insights into mRNA localization and transport processes.

Translation Regulation

Poly(A) tails are associated with translation efficiency. Longer poly(A) tails generally promote translation, while shorter ones can reduce translation rates. Understanding the relationship between poly(A) tail length and translation regulation can shed light on how gene expression is controlled at the translational level.

Post-transcriptional Gene Regulation

Poly (A) tail length changes can impact gene expression by modulating mRNA stability, translation, and localization. By studying poly(A) tail dynamics, researchers can uncover post-transcriptional gene regulatory mechanisms that influence protein production and cellular processes.

Techniques And Approaches in Poly(A) Tails Research

The precise sequence of the poly(A) tail has been challenging to decipher due to technical difficulties in sequencing repetitive sequences. However, recent advancements in high-throughput sequencing technologies have allowed researchers to gain more insights into the poly(A) tail length and sequence.


Poly(A)-Seq represents an advanced next-generation sequencing technique designed for comprehensive profiling of polyadenylation sites throughout the transcriptome. By selectively sequencing the 3' termini of mRNA molecules containing poly(A) tails, our Poly(A)-Seq service offers an extensive perspective on mRNA stability and translation efficiency.

TAIL Iso-seq (Targeted Analysis of the Isoform Landscape by RNA sequencing)

TAIL-seq is a targeted RNA sequencing method that specifically captures the poly(A) tails of mRNAs. It utilizes oligo(dT)-based priming and template switching to selectively amplify polyadenylated transcripts. By sequencing the captured fragments, TAIL-seq provides information on the poly(A) tail length and can be used to analyze the 3' end isoform diversity.

Explore our TAIL Iso-seq Service for more details in studying the relationship between transcript isoforms, expression levels, and poly(A) tail lengths.

Cap-Analysis of Gene Expression (CAGE) Sequencing

CAGE is a method used to analyze the 5' ends of capped mRNAs, allowing the identification and quantification of transcription start sites (TSSs) in a transcriptome-wide manner. It involves the conversion of capped RNA molecules into cDNA followed by deep sequencing. CAGE provides information on the precise positions of TSSs, which can help annotate gene promoters, understand transcriptional regulation, and study alternative promoter usage.

RNA immunoprecipitation (RIP) Sequencing

RIP is a technique that enables the study of RNA-protein interactions. It involves immunoprecipitating specific RNA-binding proteins (RBPs) along with their bound RNA molecules. By using antibodies specific to the RBPs of interest, RIP allows the isolation of RNA molecules associated with those proteins. The enriched RNA can then be analyzed using various downstream methods, such as qRT-PCR or high-throughput sequencing, to identify the bound RNA species and investigate their functions and regulatory roles.

Refer to our RIP-Seq Service for your next RNA-protein interaction research. Please refer to our article RIP-Seq: Introduction, Features, Workflow, and Applications.

Direct RNA Sequencing

Direct RNA sequencing, on the other hand, refers to sequencing methods that directly sequence RNA molecules without the need for prior conversion into complementary DNA (cDNA). These techniques enable the analysis of RNA sequences, including the potential sequencing of poly(A) tails. Nanopore sequencing, a long-read sequencing technology, is an example of a platform that offers direct RNA sequencing capabilities, such as Oxford Nanopore Technologies' MinION and PromethION, which have also been employed for studying poly(A) tails. These technologies enable real-time, single-molecule sequencing and can potentially provide information on both the length and sequence of the poly(A) tail.

Applications of Poly(A) Tail in RNA Sequencing

Gene Expression Analysis

The utilization of Poly(A) selected RNA sequencing provides a refined approach to quantifying gene expression levels, facilitating the analysis of differential gene expression across diverse conditions. This valuable information plays a pivotal role in comprehending cellular responses, unraveling disease mechanisms, and identifying potential therapeutic targets.

Identification of Alternative Polyadenylation Sites

The phenomenon of alternative polyadenylation gives rise to mRNA isoforms possessing varying 3' untranslated regions (UTRs). By employing Poly(A) selection in conjunction with RNA sequencing, it becomes possible to discern alternative polyadenylation sites, thereby illuminating the intricate landscape of the transcriptome and its profound influence on gene regulation.

Detection of RNA Isoforms and Splicing Variants

Poly(A) selected RNA sequencing contributes significantly to the identification of alternative splicing events, unraveling the complexity inherent in the transcriptome and advancing our understanding of post-transcriptional regulation. It enables comprehensive characterization of isoforms and facilitates the discovery of novel splice variants associated with specific cellular processes or diseases.


  1. Passmore, Lori A., and Jeff Coller. "Roles of mRNA poly (A) tails in regulation of eukaryotic gene expression." Nature Reviews Molecular Cell Biology 23.2 (2022): 93-106.
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