The vectors used in eukaryotic cells are constructed such that they can exist in both the eukaryotic cells and E. coli are called :

Options

A. Shuttle vectors
B. pBR322
C. Yeast artificial chromosome
D. Bacterial artificial chromosome

Answer

To solve the question, we need to identify the type of vector that can exist in both eukaryotic cells and E. coli. Let's analyze the options provided:

1. **Shuttle Vectors**: These are plasmids designed to replicate in two different host species, typically a eukaryotic cell and a bacterial cell like E. coli. They allow for manipulation in E. coli, which is easier, and then can be transferred to a eukaryotic system.

2. **PBR322**: This is a plasmid cloning vector that is primarily used in E. coli. It does not function in eukaryotic cells, making it an incorrect choice.

3. **Yeast Artificial Chromosome (YAC)**: YACs are designed for cloning in yeast cells, not E. coli, so this option is also incorrect.

4. **Bacterial Artificial Chromosome (BAC)**: BACs are used for cloning in bacterial cells, specifically E. coli, and are not suitable for eukaryotic cells, making this option incorrect as well.

Based on this analysis, the correct answer is **Shuttle Vectors** because they can exist and function in both eukaryotic cells and E. coli.

### Step-by-Step Solution:
1. **Identify the types of vectors**: Look at the options provided (Shuttle Vectors, PBR322, YAC, BAC).
2. **Analyze each vector**:
- **Shuttle Vectors**: Can replicate in both eukaryotic cells and E. coli.
- **PBR322**: Only works in E. coli.
- **YAC**: Only works in yeast cells.
- **BAC**: Only works in bacterial cells (E. coli).
3. **Determine the correct answer**: Since Shuttle Vectors can function in both types of cells, they are the correct choice.

### Final Answer:
The vectors used in eukaryotic cells that can exist in both eukaryotic cells and E. coli are called **Shuttle Vectors**.