Cloning and sequencing of genes encoding the TthHB8I restriction and modification enzymes: comparison with the isoschizomeric TaqI enzymes.
Genes encoding the TthHB8I restriction and modification (R-M) system from Thermus thermophilus HB8 (recognition sequence T decreases CGA) were cloned in Escherichia coli. The genes have the same transcriptional orientation, with the last 13 codons of the methyltransferase (MTase) overlapping the first 13 codons of the endonuclease (ENase). Nucleotide sequence analysis of the TthHB8I ENase revealed a single chain of 263 amino acid (aa) residues that share a 77% identity with the corrected isoschizomeric TaqI ENase. Likewise, the Tth MTase (428 aa) shares a 79% identity with the corrected sequence of the TaqI MTase. This high degree of aa conservation suggests a common origin between the Taq and Tth R-M systems. However, codon usage and G+C content for the R-M genes differed markedly from that of other cloned Thermus genes. This suggests that these R-M genes were only recently introduced into the genus Thermus.
Barany
F
F
Department of Microbiology, Hearst Microbiology Research Center, Cornell University Medical College, New York, NY 10021.
Danzitz
M
M
Zebala
J
J
Mayer
A
A
D000595:Amino Acid Sequence; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D003062:Codon / Q000235:genetics*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000737:chemistry / Q000235:genetics*; D005807:Genes, Overlapping / Q000235:genetics*; D008969:Molecular Sequence Data; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000737:chemistry / Q000235:genetics*; D013824:Thermus / Q000201:enzymology* / Q000235:genetics
D003062:Codon; C059680:DNA modification methylase TaqI; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D015252:Deoxyribonucleases, Type II Site-Specific; C027046:TCGA-specific type II deoxyribonucleases