Cotranscriptionally

Cotranscriptionally describes processes that occur while RNA is being synthesized from a DNA template by RNA polymerase. In this sense, RNA maturation, assembly with proteins, folding, and quality control can begin before transcription is finished. Cotranscriptional events help coordinate gene expression and ensure proper RNA structure and function.

In eukaryotes, many RNA processing steps are cotranscriptional. The 5' end of a nascent transcript often receives a cap soon after transcription initiation, which protects RNA and aids translation. Splicing of introns can commence during elongation and is influenced by transcriptional speed and chromatin context. Cleavage and polyadenylation at the 3' end, along with recruitment of termination and export factors, can occur while the transcript is still being produced. These cotranscriptional events result in messenger RNAs that are already associated with processing complexes as they are exported from the nucleus.

In bacteria, transcription and translation are physically coupled, allowing ribosomes to begin translating mRNA before transcription is complete. This cotranscriptional coupling is a central aspect of bacterial gene expression. RNA folding and regulatory elements can also form cotranscriptionally, and riboswitches or attenuation mechanisms can respond to transcriptional kinetics.

Studying cotranscriptional processes uses techniques that capture nascent RNAs and processing factor associations, such as nascent RNA sequencing approaches and chromatin-associated RNA analyses. Understanding cotranscriptional coordination illuminates how transcription rate, chromatin state, and RNA folding influence splicing, 3' end formation, and gene expression fidelity. Disruptions in cotranscriptional coordination have been linked to diseases and developmental defects in eukaryotes.