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The brilliant contributions of workers at the Institut Pasteur have revealed the existence of a specific, genetically controlled t;ransport system that mediates the uptake of lactose in Escherichia coli. Work on this transport systemn. has been t,he subject of numerous reports anid reviews.'.--' We have recently reported evidence that a membrane-bouind protein distinct from 0-galactosidase and thiogalactoside transacetylase (the two previously characterized proteins of the lac system) is an essential compouient of the transport system.6 Unitil the exact function of this proteini is made clear, the nooncommittal. designation memnbrane protein (il protein) seems appropriate. In our working model6 of the 3-galactoside transport system, the All protein is that componenrt in. the membrane that specifically binds certain. galactosides, forming a complex of the M\/tichaelis-lVfenten type. The sugar then passes through the membrane as the 3-galactoside-Al complex. In the presenlce of sources of metabolic energy, the protein is postulated to undergo transformation to a fornm designated Mli having little affinity for the sugar, thus leading to accumulation of the sugar withiii the cell. This working hypothesis is described in greater detail elsewhere.7 The function of the All proteirn in. mediating the transport of substrates such as o-nitrophenyl-0-galactoside (ONPG)8 is destroyed when cells are treated with Nethylmaleimide. However, the protei.n has a high affiniity for thiodigalactoside (TDG) and when the protein is complexed with this sugar, it is protected against N-ethylmaleimide.A These properties are the basis of a specific chemical method for the detectioni of the protein in cell-free fractions of E. coli. In the present publication we wish to report the results of studies oil the genetic control of the .11 protein, which. indicate that the protein is coded by the y genie of the lac operon.I Further evidence that the proteini. is localized in the spheroplast membrane fraction of the cell has also been obtained. A preliminary estimate of the minimum number of functional subunits of .11/ protein per cell has also been made.

GENETIC CONTROL OF THE MEMBRANE PROTEIN COMPONENT OF THE LACTOSE TRANSPORT SYSTEM OF Escherichia coli