This behavior is different from any of the lac mutations that we have discussed. the interpretation is that MalT encodes a diffusible gene product(not a site on DNA)that is required for activation of transcription of the Mal operon. This type of gene is usually called an activator. As shown in the diagram below, maltose binds to the Mal activator protein causing a conformational change in Malt allowing it to bind near to the promoter and to stimulate transcription. Note that the genes required for maltose uptake are located in an operon elsewhere on the chromosome but these genes are also regulated by MalT The Mal Operon activator maltodextrin protein amylomaltose RNA polymerase Mat P initiator MaIP MalE romoter induc This model requires a site, called the initiator, which is where the activator binds near site should behave in dominance and cis/trans tests, you will see why in practice itis the promoter to activate transcription. If you think about how mutations in an initiate difficult to distinguish initiator site mutations from promoter mutations It is also possible to isolate super activator"mutants that will bind to the initiator site and activate transcription regardless of whether the inducer maltose is present. Such alleles of the MalT gene are called malTe and their properties are given below -maltose +maltose Interpretation Malte is constitutive MalTc/f MalT+ Maltc is dominant MalTe MalE/FMT+MQr◆ MalTe is trans-acting MalTc MaIQ/ FMaIT* MaIQ.◆ For a multimeric activator it should also be possible to isolate activator-d mutants that will interfere with the binding of wild-type subunits to the initiator site. Actually Malm-d mutants have not been isolated, probably because Malt is a monomerThis behavior is different from any of the Lac mutations that we have discussed. The interpretation is that MalT encodes a diffusible gene product (not a site on DNA) that is required for activation of transcription of the Mal operon. This type of gene is usually called an activator. As shown in the diagram below, maltose binds to the MalTactivator protein causing a conformational change in MalT allowing it to bind near to the promoter and to stimulate transcription. Note that the genes required for maltose uptake are located in an operon elsewhere on the chromosome, but these genes are also regulated by MalT. The Mal Operon activator maltodextrin MalT MalP MalQ P promoter initiator protein phosphorylase amylomaltase + inducer RNA polymerase (maltose) This model requires a site, called the initiator, which is where the activator binds near the promoter to activate transcription. If you think about how mutations in an initiator site should behave in dominance and cis/trans tests, you will see why in practice it is difficult to distinguish initiator site mutations from promoter mutations. It is also possible to isolate “super activator” mutants that will bind to the initiator site and activate transcription regardless of whether the inducer maltose is present. Such alleles of the MalT gene are called MalTc and their properties are given below. –maltose +maltose Interpretation MalTc + + MalTcis constitutive MalTc’/ F MalT+ + + MalTcis dominant MalTc MalQ+/ F’ MalT+ MalQ– + + MalTcis trans-acting MalTc ’ MalQ–/ F MalT+ MalQ+ + + For a multimeric activator it should also be possible to isolate activator-d mutants that will interfere with the binding of wild-type subunits to the initiator site. Actually MalT-d mutants have not been isolated, probably because MalT is a monomer