What is a silencer element?

• A. A DNA sequence that binds repressors to decrease transcription.
• B. A sequence that increases transcription by activating RNA polymerase.
• C. A site that initiates translation.
• D. A site that terminates transcription.

Answer: (A)

A silencer element is a DNA sequence that binds transcriptional repressors to reduce gene transcription. When a repressor protein attaches to this site, it hinders the assembly or activity of the transcription machinery at the promoter, or it promotes a chromatin state that makes the DNA less accessible, effectively dialing down expression. This explains why it decreases transcription rather than increasing it or affecting translation or termination.

The other ideas don’t fit: an element that boosts transcription by activating RNA polymerase is an enhancer, not a silencer. A site that initiates translation relates to the ribosome recognizing mRNA, not to transcription control. A site that terminates transcription is a terminator, which ends transcription, not represses it at the promoter.