Local variability of the phosphoglycerate kinase-triosephosphate isomerasefusion protein from Thermotoga maritima MSB 8

The pgk-tpi gene locus of Thermotoga maritime encodes both phosphoglycerate kinase (PGK) and a bienzyme complex consisting of a fusion protein of PGK with triosephosphate isomerase (TIM). No separate tpi gene for TIM is prese nt in T. maritima. A frame-shift at the end of the pgk gene has been previo usly proposed as a mechanism to regulate the expression of the two protein variants [Schurig et at, EMBO J. 14 (1995), 442-451]. Surprisingly, the com plete T. maritima genome was found to contain a pgk-tpi sequence not requir ing the proposed frameshift mechanism. To clarify the apparent discrepancy, a variety of DNA sequencing techniques were applied, disclosing an anomalo us local variability in the pgk-tpi fusion region. The comparison of differ ent DNA samples and the mass spectrometric analysis of the amino acid seque nce of the natural fusion protein from T. maritima MSB8 confirmed the local variability of the DNA variants. Since not all peptide masses could be ass igned, further variations are conceivable, suggesting an even higher hetero geneity of the T. maritima MSB8 strain.