In the absence of lactose, the repressor protein encoded by the I gene binds to the lac operator and prevents transcription. Binding of allolactose to the repressor causes it to leave the operator. This enables RNA polymerase to transcribe the three genes of the operon.
A tough-skinned tropical fruit, the mango features a sweet, orange- to red-color flesh inside when ripe. Kensington pride, Kent, Palmer and sensation are only a few of the many varieties of mango available through groceries and markets.
Climacteric fruits like plums will ripen off the tree. A casaba melon is ripe when the blossom end is slightly yielding. The mamey fruit should be soft to the touch when ripe. Bananas ripen off the parent plant. A variety of ripe apples. Grapes will not ripen any more after they are picked from their vine. Storing fruit in the refrigerator can prolong its shelf life. Tangerines should look plump and juicy when they are ripe.