Final answer:
Temperature-sensitive proteins utilized in the study of secretory pathways are only active at low and inactive at high temperatures. This provides a useful tool for studying the cellular mechanisms of protein trafficking.
Step-by-step explanation:
Temperature-sensitive proteins used to study the secretory pathway in the context of VSV-G fusion proteins and mutant yeast strains are designed to be functional at a permissive temperature and dysfunctional (or inactive) at a restrictive temperature. The characteristics of these proteins should match the description of being functional under certain temperature conditions while losing their function when these conditions are altered.
The correct characteristic of these temperature-sensitive proteins is that they are only active at low temperatures. At higher, non-permissive temperatures, these proteins become nonfunctional, which can be used experimentally to understand the mechanisms of protein trafficking within a cell. This is because cellular processes, such as the secretory pathway, can be observed under normal conditions and then be interrupted by shifting to a higher temperature, thereby inactivating the temperature-sensitive proteins and halting the process they are involved in.
As explained in some examples from biology, temperature can regulate gene expression, and temperature-sensitive mutations can cause phenotypic changes in response to environmental temperature shifts. This principle leverages the heat-induced misfolding of proteins to study biological processes.