Group IIC intron mobility into attC sites involves a bulged DNA stem-loop motif

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Bacterial group IIC introns are ribozymes often found downstream of transcriptional terminators.
• Class IIC-attC introns are a subset that target specific recombination sites (attC) for integron integrases.
• attC sites feature conserved inverted repeats flanking a variable palindromic central region.

Purpose of the Study:

• To investigate the in vivo recognition mechanism of the attC(aadA1) stem-loop motif by the Serratia marcescens intron (S.ma.I2).
• To determine the DNA sequence and structural features critical for S.ma.I2 intron homing specificity.

Main Methods:

• Polymerase Chain Reaction (PCR) was employed to analyze intron mobility.
• Colony patch hybridization was used to assess intron insertion frequencies.
• Mutagenesis of attC sites was performed to evaluate recognition determinants.

Main Results:

• S.ma.I2 intron mobility into wild-type attC sites occurred at 18% frequency, influenced by DNA replication direction.
• Intron mobility into mutant attC sites indicated recognition of unwound DNA stem-loop motifs.
• High homing frequency required a bulged base within the attC stem-loop structure.
• IBS1/IBS3 motifs and two bulge bases on the attC bottom strand were identified as key determinants for S.ma.I2 homing specificity.

Conclusions:

• S.ma.I2 intron recognition of attC sites is mediated by a bulged hairpin DNA motif, not a specific sequence.
• This motif recognition mechanism allows class IIC-attC introns to tolerate variations in attC sequences.
• The findings elucidate the molecular basis for site-specific homing of IIC-attC introns.