Final answer:
CI levels are low in λ phage when it transitions from the lysogenic to the lytic cycle, which is regulated by the host cell's environment and resources.
Step-by-step explanation:
The CI levels in λ phage are low due to the regulation of its life cycle. The λ phage can enter either a lysogenic or a lytic cycle when it infects a host cell. During the lysogenic cycle, the phage DNA integrates into the host genome and is replicated along with it.
The CI protein serves as a repressor that maintains the phage in a dormant state by preventing the expression of genes necessary for entering the lytic cycle.
However, when certain conditions are met, such as stress to the host cell, the levels of CI protein can decrease, leading to the induction of the lytic cycle, where the phage DNA is expressed, new phages are produced, and the host cell is ultimately lysed.
This switch is a finely tuned process that is affected by multiple factors including the host cell environment and the availability of resources.