CLONING AND SEQUENCING OF ASPARTATE-AMINOTRANSFERASE FROM THERMUS-AQUATICUS YT1

A 39-base olgonucleotide ''guessmer'' probe, based on partial N-termin al sequence analysis of the aspartate aminotransferase purified from T hermus aquaticus strain YT1, was used to screen a genomic library prep ared hom T. aquaticus DNA. ih 1842 bp DNA fragment was isolated that p roved to contain the coding sequence for the aspartate aminotransferas e. The gene is 1152 bases long and codes for a protein of 383 amino ac id residues, The amino acid sequence obtained showed 88.7%, 45.1% and 32.9% identity of sequence with those of thermostable aspartate aminot ransferases from T. thermophilus, Bacillus YM2, and Sulfolobus bus sol fataricus, respectively. Ht showed 39.1% identify with one of the gene products tenatatively identified as aspartate aminotransferase from t he methanogenic archaebacterium Methanococcus jannaschii. Neither the amino acid compositions nor the aligned amino acid sequences provides any obvious clue as to the origin of thermal stability in this group o f enzymes. (C) 1997 Academic Press.