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Abstract The pgktpi gene locus of Thermotoga maritima 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 present in T. maritima. A
frameshift at the end of the pgk gene has been previously
proposed as a mechanism to regulate the expression
of the two protein variants [Schurig et al.,
EMBO J. 14 (1995), 442 451]. Surprisingly, the complete
T. maritima genome was found to contain a pgktpi
sequence not requiring the proposed frameshift
mechanism. To clarify the apparent discrepancy, a variety
of DNA sequencing techniques were applied,
disclosing an anomalous local variability in the pgktpi
fusion region. The comparison of different DNA
samples and the mass spectrometric analysis of the
amino acid sequence of the natural fusion protein
from T. maritima MSB8 confirmed the local variability
of the DNA variants. Since not all peptide masses
could be assigned, further variations are conceivable,
suggesting an even higher heterogeneity of the T.
maritima MSB8 strain.
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