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A dichotomous epigenetic mechanism governs expression of the LlaJI restriction/modification system
Author(s) -
O'Driscoll Jonathan,
Fitzgerald Gerald F.,
van Sinderen Douwe
Publication year - 2005
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.04769.x
Subject(s) - biology , epigenetics , genetics , dna methylation , repressor , operon , gene , recognition sequence , promoter , psychological repression , regulation of gene expression , epigenetics of physical exercise , gene expression , microbiology and biotechnology , restriction enzyme , mutant
Summary The LlaJI restriction/modification (R/M) system is comprised of two 5mC MTase‐encoding genes, llaJIM1 and llaJIM2 , and two genes required for restriction activity, llaJIR1 and llaJIR2 . Here, we report the molecular mechanism by which this R/M system is transcriptionally regulated. The recognition sequence for the LlaJI MTases was deduced to be 5′GACGC′3 for M1.LlaJI and 5′GCGTC′3 for M2.LlaJI, thus together constituting an asymmetric complementary recognition site. Two recognition sequences for both LlaJI MTases are present within the LlaJI promoter region, indicative of an epigenetic role. Following in vivo analysis of expression of the LlaJI promoter, we established that both LlaJI MTases were required for complete transcriptional repression. A mutational analysis and DNA binding studies of this promoter revealed that the methylation of two specific cytosines by M2.LlaJI within this region was required to trigger the specific and high affinity binding of M1.LlaJI, which serves to regulate expression of the LlaJI operon. This regulatory system therefore represents the amalgamation of an epigenetic stimulation coupled to the formation of a MTase/repressor:promoter complex.