in a wild-type e coli cell, which of the following genes is constitutively expressed?

In a wild-type E. coli cell, housekeeping genes (such as those encoding RNA polymerase core subunits, ribosomal RNAs, ribosomal proteins, and enzymes of central metabolism like glycolysis) are constitutively expressed.

Key idea

• Constitutive expression means the gene is transcribed at a relatively constant level, independent of specific environmental inducers or repressors.

• In wild-type E. coli , this applies mainly to essential “housekeeping” functions , not to typical inducible operons like lac or trp , which are tightly regulated by nutrients (lactose, tryptophan, etc.).

Common exam-style options

When this question appears in genetics or microbiology exams, the constitutively expressed choice is usually something like:

• A gene encoding RNA polymerase subunit (e.g., rpoB/rpoC)
• A ribosomal RNA gene (rRNA, e.g., rrn operons)
• A core ribosomal protein gene
• A central metabolism enzyme (e.g., glycolytic enzyme)

Whereas genes like lacZ , trpE , or other catabolic/biosynthetic operon genes are not constitutive in a wild-type strain; they are induced or repressed depending on substrate or amino acid availability.

How to pick the answer

• If the options include a clear housekeeping gene (e.g., “rRNA gene”, “RNA polymerase gene”, “gene for a ribosomal protein”) alongside regulatory/inducible genes (lac , trp , stress-response), choose the housekeeping gene as the constitutively expressed one.

TL;DR: In a wild-type E. coli , the constitutively expressed gene among typical choices is the one coding for a basic housekeeping function (rRNA, ribosomal protein, or RNA polymerase), not lac or trp operon genes.

Information gathered from public forums or data available on the internet and portrayed here.