PHOSPHOSERINE AMINOTRANSFERASE FROM BACILLUS-CIRCULANS SUBSP ALKALOPHILUS - PURIFICATION, GENE CLONING AND SEQUENCING

Two peaks of aspartate aminotransferase (AspAT) catalytic activity wer e observed during DEAE chromatography of a protein extract from alkalo philic B. circulans. The enzyme purified from the major peak appeared to be not aspartate but phosphoserine aminotransferase (PSAT) with a c onsiderably high AspAT side activity. The sequence of the enzyme N-ter minus was determined, and the PSAT gene was cloned as two separate fra gments. DNA sequencing revealed the open reading frame for the PSAT st arting from TTG, putative ribosomal binding site and terminator of tra nscription. The PSAT gene encodes a protein of 361 amino acids (M(r) 3 9 793) which shows moderate homology to other known phosphoserine amin otransferases (36-46% of identity, 60-64% of similarity). The PSAT fro m the alkalophile shares with all of them the consensus sequence patte rn around the pyridoxal S-phosphate attachment site.