Rut sites are rich in which nucleotide?

Rut sites, or "Rho utilization sites," are critical regions in certain transcripts that facilitate the termination of transcription by the Rho protein, a crucial factor in bacterial gene expression. Rut sites are characteristically rich in cytosine (C). The presence of an over-abundance of cytosine residues aids in the formation of specific RNA secondary structures that can interact with the Rho factor, promoting its binding and advancing the transcription termination process.

This high concentration of cytosine helps create the proper conditions for Rho to bind to the RNA transcript and proceed with its activity after the RNA polymerase has paused, subsequently leading to the termination of RNA synthesis. The specificity of Rut sites for cytosine is fundamental for understanding bacterial gene regulation and the mechanisms behind transcription termination.