Which gene is linked to the common promoter lacY?

The gene linked to the common promoter lacY is indeed the one that codes for permease. The lac operon, which is a classic example of gene regulation in prokaryotes, comprises three structural genes: lacZ, lacY, and lacA.

LacY specifically encodes for the enzyme permease, which facilitates the transport of lactose into the bacterial cell. This transport is crucial because, in order for the other enzymes (such as beta-galactosidase, encoded by lacZ) to metabolize lactose, it must first enter the cell.

The promoter of the lac operon is where regulatory proteins can bind and control the expression of these genes based on the presence or absence of lactose and glucose. When lactose is present, it binds to the repressor protein (which is a different gene) and allows the transcription of lacY along with the other operon genes. Thus, the connection between lacY and its corresponding permease function is essential for the entire lactose metabolism process in bacteria.

Understanding this relationship highlights the coordinated regulation of gene expression in the lac operon, emphasizing how permease (coded by lacY) plays a pivotal role in lactose uptake.