In bacteria, regulation of gene expression is usually affected through ................. .

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Gene Expression Regulation:**
- Gene expression regulation is crucial for controlling how genes are turned on or off in an organism. In bacteria, this regulation is particularly important due to their simple structure and rapid growth.

2. **Identifying the Levels of Regulation:**
- Gene expression can be regulated at multiple levels: transcription, splicing, mRNA transport, and translation. However, in bacteria, certain levels are not applicable due to their prokaryotic nature.

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