TheBsaHI Restriction-Modification System: Cloning, Sequencing and Analysis of Conserved Motifs
Restriction and modification enzymes typically recognise short DNA sequences of between two and eight bases in length. Understanding the mechanism of this recognition represents a significant challenge that we begin to address for the BsaHI restriction-modification system, which recognises the six base sequence GRCGYC.
Results: The DNA sequences of the genes for the BsaHI methyltransferase, bsaHIM, and restriction endonuclease, bsaHIR, have been determined (GenBank accession #EU386360), cloned and expressed in E.coli.
Both the restriction endonuclease and methyltransferase enzymes share significant homology with a group of 6 other enzymes comprising the RM systems HgiDI and HgiGI and the putative HindVP, NlaCORFDP, NpuORFC228P and SplZORFNP RM systems. A sequence alignment of these homologues shows that their amino acid sequences are largely conserved and highlights several motifs of interest.
One such conserved motif was identified at the C-terminal end of the bsaHIR gene as a potential DNA-recognising region of the enzyme. A mutational analysis of these amino acids is consistent with this assignment.
Sequence alignment of the methyltransferase gene reveals a motif that may be used as a diagnostic tool to define the recognition sequences of the cytosine C5 methyltransferases.
Conclusions: We have identified a region of the R.BsaHI enzyme that is likely involved in DNA recognition.
Analysis of the amino acid sequence of the BsaHI methyltransferase enzyme led us to propose two new motifs that can be used in the diagnosis of the recognition sequence of the cytosine C5-methyltransferases.
Author: Robert K Neely and Richard J Roberts
Credits/Source: BMC Molecular Biology 2008, 9:48
Published on: 2008-05-15
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