Which of the following does not control gene expression?

To determine which of the following does not control gene expression, we need to analyze each option and identify the one that does not play a role in regulating gene expression. Here are the options:

1. Transcription factors: Transcription factors are proteins that bind to specific DNA sequences and regulate the transcription of genes. They play a crucial role in controlling gene expression.

2. Promoters: Promoters are DNA sequences that are located upstream of a gene and serve as binding sites for transcription factors. They initiate the transcription process and are essential for gene expression.

3. Ribosomes: Ribosomes are cellular structures responsible for protein synthesis. They translate the mRNA produced during transcription into proteins, which are key players in gene expression.

4. Introns: Introns are non-coding regions within a gene that are transcribed but not translated into proteins. They are involved in alternative splicing, which can generate different protein isoforms, thus influencing gene expression.

Based on the options provided, it appears that ribosomes do not directly control gene expression. While they are involved in protein synthesis, they do not regulate the transcription or translation processes. Therefore, ribosomes can be identified as the option that does not control gene expression.