BsuBI--an isospecific restriction and modification system of PstI: characterization of the BsuBI genes and enzymes.
The enzymes of the Bacillus subtilis BsuBI restriction/modification (R/M) system recognize the target sequence 5'CTGCAG. The genes of the BsuBI R/M system have been cloned and sequenced and their products have been characterized following overexpression and purification. The gene of the BsuBI DNA methyltransferase (M.BsuBI) consists of 1503 bp, encoding a protein of 501 amino acids with a calculated M(r) of 57.2 kD. The gene of the restriction endonuclease (R.BsuBI), comprising 948 bp, codes for a protein of 316 amino acids with a predicted M(r) of 36.2 kD. M.BsuBI modifies the adenine (A) residue of the BsuBI target site, thus representing the first A-N6-DNA methyltransferase identified in B. subtilis. Like R.PstI, R.BsuBI cleaves between the A residue and the 3' terminal G of the target site. Both enzymes of the BsuBI R/M system are, therefore, functionally identical with those of the PstI R/M system, encoded by the Gram negative species Providencia stuartii. This functional equivalence coincides with a pronounced similarity of the BsuBI/PstI DNA methyltransferases (41% amino acid identity) and restriction endonucleases (46% amino acid identity). Since the genes are also very similar (58% nucleotide identity), the BsuBI and PstI R/M systems apparently have a common evolutionary origin. In spite of the sequence conservation the gene organization is strikingly different in the two R/M systems. While the genes of the PstI R/M system are separated and transcribed divergently, the genes of the BsuBI R/M system are transcribed in the same direction, with the 3' end of the M gene overlapping the 5' end of the R gene by 17 bp.
Xu
G L
GL
Max-Planck-Institut für Molekulare Genetik, Berlin, Germany.
Kapfer
W
W
Walter
J
J
Trautner
T A
TA
D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics*; D001483:Base Sequence; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D015698:Genomic Library; D008745:Methylation; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D015183:Restriction Mapping; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic
D004269:DNA, Bacterial; D009838:Oligodeoxyribonucleotides; C059681:DNA modification methylase PstI; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C024388:CTGCAG-specific type II deoxyribonucleases; D015252:Deoxyribonucleases, Type II Site-Specific