Bacillus subtilis phage SPR codes for a DNA methyltransferase with triple sequence specificity

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Temperate phages like SPR play crucial roles in bacterial genetics.
• DNA methyltransferases are key enzymes in epigenetic regulation and host-defense mechanisms.

Purpose of the Study:

• To characterize the substrate specificity of the SPR phage DNA methyltransferase.
• To investigate the genetic basis of methylation abilities in SPR phage mutants.

Main Methods:

• In vitro methylation assays using purified SPR methyltransferase.
• In vivo methylation analysis in Bacillus subtilis.
• Characterization of mutant phages (SPR19, SPR83, SPR26) with defects in methylation.

Main Results:

• SPR methyltransferase efficiently methylates GGCC, CCGG, and CC(A/T)GG DNA sequences.
• Methylation of CC(A/T)GG sites confers protection against restriction enzymes EcoRII and ApyI.
• Mutant phages demonstrate genetically separable methylation activities, with SPR26 lacking all tested methylation abilities.

Conclusions:

• The SPR methyltransferase exhibits multiple, genetically distinguishable substrate specificities.
• These findings provide insights into phage-DNA interactions and epigenetic modifications.