Basal level of transcription refers to
Basal transcription refers to low constitutive synthesis occurring without induction due to imperfect repressor-operator occupancy governed by binding kinetics. LacI occasionally dissociates permitting brief promoter vacancies where RNA polymerase initiates transcription producing few molecules per generation. Leakiness yields two to five copies of LacY permease and beta-galactosidase per cell even under repression. Such sentinel molecules are crucial because they allow initial lactose import and intracellular allolactose generation enabling rapid autocatalytic activation upon lactose appearan
Ref: Alberts Molecular Biology of the Cell 6th ed. Chapter 7 – leaky basal transcription provides permease for initial inducer import.