title: Cro regulatory protein specified by bacteriophage lambda. Structure, DNA-binding, and repression of RNA synthesis.
abstract: The Cro protein specified by bacteriophage lambda is a repressor of the genes expressed early in phage development and is required for a normal late stage of lytic growth. We have purified Cro protein to virtual homogeneity and analyzed its structure and properties as a DNA-binding protein and repressor of RNA synthesis. To confirm that the protein is the product of the cro gene, we have also shown that a missense mutation in the cro gene leads to a product that is more temperature- and salt-sensitive in its DNA-binding property. As purified, Cro protein is a dimer of identical subunits of molecular weight 8600. The purified protein binds to lambda-DNA carrying the specific binding sites (operators oL and oR) with an estimated dissociation constant of 10(-10) M to 10(-11) M; there is also weaker binding to other sites on DNA, as found for other DNA-binding regulatory proteins. In a purified transcription system, the Cro protein is an effective and specific repressor of RNA synthesis from the N and cro genes; thus Cro is an autorepressor which regulates its own synthesis. A comparison of the properties of the two lambda repressor proteins, cI and Cro, indicates that cI is a "strong repressor" specialized for complete turnoff of lytic functions needed for the maintenance of lysogeny, whereas Cro is a "weak repressor" specialized for a gradual turnoff of early viral genes that potentiates the late stage of lytic development.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D003090:Coliphages / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004355:Drug Stability; D004794:Enzyme Repression; D004926:Escherichia coli / Q000378:metabolism; D005796:Genes; D007700:Kinetics; D008970:Molecular Weight; D009154:Mutation; D009994:Osmolar Concentration; D011485:Protein Binding; D012367:RNA, Viral / Q000096:biosynthesis*; D013696:Temperature; D014764:Viral Proteins / Q000302:isolation & purification / Q000502:physiology
chemical_list: D000596:Amino Acids; D004279:DNA, Viral; D012367:RNA, Viral; D014764:Viral Proteins; D012321:DNA-Directed RNA Polymerases