Final answer:
Quorum sensing in Vibrio harveyi regulates bioluminescence through autoinducing proteins that prevent a sigma factor from binding to Lux mRNA, allowing translation of bioluminescent genes when bacterial population density is high.
Step-by-step explanation:
The bioluminescence in Vibrio harveyi is controlled by a mechanism called quorum sensing. This process involves bacterial cell-cell communication through signaling molecules called autoinducers. When the bacterial population reaches a certain density, these autoinducers reach a threshold concentration, which then allows the bacteria to synchronously express specific genes, including those responsible for bioluminescence. The question is about which of the listed options is responsible for preventing the sigma factor from binding to Lux mRNA, thus permitting the translation of bioluminescent genes in Vibrio harveyi. The correct answer is autoinducing proteins (4), as they are part of the quorum sensing system that regulates the expression of the bioluminescent genes.