Crystal structures of the E. coli transcription initiation complexes with a complete bubble

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Transcription initiation is a crucial step in gene expression, involving RNA polymerase binding to promoter DNA.
• This process includes forming an initiation complex with a DNA bubble and often involves abortive RNA synthesis cycles before productive elongation.

Purpose of the Study:

• To elucidate the structural mechanisms of transcription initiation in E. coli.
• To understand how RNA polymerase recognizes promoter DNA and interacts with nascent RNA during initiation.

Main Methods:

• X-ray crystallography was used to determine the structures of E. coli transcription initiation complexes.
• Structures were resolved at approximately 6-Å resolution, featuring complete transcription bubbles and de novo synthesized RNA oligonucleotides.

Main Results:

• The crystal structures reveal how RNA polymerase recognizes DNA promoters with varying spacer lengths.
• A bridging interaction between the nascent RNA's 5'-triphosphate and the σ factor was identified, potentially stabilizing early RNA-DNA hybrids.
• The conformation of RNA oligonucleotides and DNA strand paths within the complexes were visualized.

Conclusions:

• The findings provide structural insights into the recognition of promoter DNA by RNA polymerase.
• The identified RNA-σ factor interaction sheds light on stabilizing short RNA-DNA hybrids during initiation.
• The study offers mechanistic understanding of the regulation of abortive versus productive RNA synthesis.