Which gene of lac operon is always functioning ? Mention its product.

Explanation

### Step-by-Step Solution:

1. **Understanding the Lac Operon**: The lac operon is a set of genes in bacteria, particularly E. coli, that are involved in the transport and metabolism of lactose. It consists of several genes that work together under the control of a single promoter.

2. **Identifying the Genes in the Lac Operon**: The main genes in the lac operon include:
- **lacZ**: Codes for β-galactosidase, which breaks down lactose into glucose and galactose.
- **lacY**: Codes for permease, which facilitates the entry of lactose into the cell.
- **lacA**: Codes for transacetylase, which is involved in the metabolism of lactose.
...