부산대학교 도서관

KorB protein (358 amino acids) binds to 12 highly conserved sequences on the RK2 genome and co-ordinates the expression of at least five operons encoding genes for stable inheritance and plasmid transfer. KorB represses the trfA , korA and klaA promoters where it binds 4 bp upstream of the -35 region (class I KorB operators, OB ). We show here that KorB on its own can also repress the trbA , trbB , kfrA and kleA promoters where OB is between 80 and 189 bp away from the transcription start point (class II operator). A C-terminal deletion of 17 amino acids resulted in the loss of KorB's ability to repress through class II operator but not through class I operator. This deletion reduced multimerization of His6 -tailed KorB protein in vitro and greatly reduced binding specificity for fragments containing OB sequences. At the trbBp region, where OB 9 lies 189 bp upstream of the transcription start point, mutagenesis of a proposed secondary binding site overlapping the trbBp -35 region had no effect on the ability of KorB to repress trbBp . Nevertheless, gel retardation analysis showed that KorB binding is promoted by sequences upstream and downstream of OB 9 and that KorB can form higher order complexes on DNA. However, DNase I footprinting suggested that RNA polymerase may interact directly with KorB bound at OB 9 and implied that contacts between these proteins could be responsible for the action of KorB at a distance. [ABSTRACT FROM AUTHOR]