Effects of codon usage on gene expression are promoter context dependent

Area of Science:

• Genomics
• Molecular Biology
• Gene Regulation

Background:

• Codon usage bias is a universal genomic feature affecting gene expression.
• Genome-wide correlations between codon usage and mRNA levels are minimal in mammals, questioning its significance.
• Gene-specific regulation may obscure the true impact of codon usage on gene expression.

Purpose of the Study:

• To investigate the promoter-dependent regulation of codon usage effects on mRNA expression.
• To elucidate the mechanisms by which promoters influence codon usage-mediated gene expression.
• To determine the role of promoters in mediating transcription-dependent codon usage effects.

Main Methods:

• Comparative analysis of genome-wide codon usage and mRNA correlations in constitutively vs. differentially expressed genes.
• Experimental manipulation in Drosophila S2 cells to assess promoter-specific effects on gene expression.
• Identification of specific promoter elements (e.g., Hsp70 promoter element) involved in repressing codon usage effects.
• Analysis of transcriptional regulation, including histone modifications, nucleosome densities, and premature termination.

Main Results:

• Constitutively expressed genes show higher genome-wide codon usage-mRNA correlations than differentially expressed genes across species.
• Promoter regions, particularly downstream of core promoters, can repress codon usage effects on mRNA levels in differentially expressed genes.
• A specific element within the Hsp70 promoter was found to be essential and sufficient for this repression.
• Promoter-dependent effects are linked to transcriptional regulation via histone modifications, nucleosome positioning, and premature termination.

Conclusions:

• Promoters play a critical role in determining whether codon usage influences gene expression.
• Gene expression regulation by codon usage is largely transcription-dependent and promoter-mediated.
• Understanding promoter function is key to deciphering the impact of codon usage bias on gene regulation.