What is one disadvantage of using GFP as a marker?

Using GFP as a marker has several advantages, but one notable disadvantage is its potential to interfere with cellular processes when overexpressed. When a gene encoding GFP is introduced into a cell, particularly at high expression levels, it may disrupt normal cellular functions. This can occur because the tagged protein may compete for resources, alter protein interactions, or affect the overall metabolism of the cell. Cells may not be able to correctly fold or localize their native proteins due to the presence of excess GFP, leading to results that do not accurately reflect the true cellular environment or processes.

In contrast, the other options have their limitations—GFP is generally not considered toxic to cells at customary expression levels, it fluoresces well under proper conditions, and it can typically be expressed effectively in bacteria, making them less relevant as disadvantages. The understanding of GFP's potential impact on cellular physiology is critical for researchers to consider when designing experiments and interpreting results introduced through this fluorescent protein marker.