Readthroughtranscripts

Readthrough transcripts are RNA molecules produced when RNA polymerase II extends transcription beyond the canonical termination site of an upstream gene, sometimes into a downstream gene or adjacent genomic region. These transcripts can take the form of extended monocistronic RNAs, or bicistronic transcripts that join exons from two neighboring genes. They differ from standard mRNAs in that they contain sequence beyond the expected gene boundary and may, in some cases, span two coding regions.

Readthrough can arise through several mechanisms. Transcriptional readthrough occurs when termination signals are weak or skipped, allowing RNA polymerase II to continue beyond the polyadenylation site. Alternative splicing can also connect exons across gene boundaries, producing transcripts that incorporate sequences from adjacent genes. Additionally, transcriptional interference or promoter activities downstream of a gene can contribute to readthrough events. These events have been observed in humans and other eukaryotes and can vary with tissue type and physiological conditions.

The resulting transcripts can be noncoding or may carry open reading frames that extend across the boundary, yielding potential fusion proteins if the reading frame is preserved. Many readthrough transcripts are polyadenylated and appear in the cytoplasm, while others are unstable and subject to degradation. They are studied for their regulatory roles, including possible effects on neighboring gene expression, chromatin state, and transcript stability. Detection generally relies on RNA sequencing and targeted validation methods such as RT-PCR.

See also: transcriptional readthrough, bicistronic transcript, long noncoding RNA.