Spontaneous Mutant Lacking GroEL1, a Dispensable Chaperone

Proteome analysis of Corynebacterium glutamicum ATCC 13032 showed that levels of several proteins increased drastically in response to heat shock. These proteins were identified as DnaK, GroEL1, GroEL2, ClpB, GrpE, and PoxB, and their heat response was in agreement with previous transcriptomic results. A major heat-induced protein was absent in the proteome of strain 13032B of C. glutamicum, used for genome sequencing in Germany, compared with the wild-type ATCC 13032 strain. The missing protein was identified as GroEL1 by matrix-assisted laser desorption ionization–time of flight peptide mass fingerprinting, and the mutation was found to be due to an insertion sequence, IsCg1, that was integrated at position 327 downstream of the translation start codon of the groEL1 gene, resulting in a truncated transcript of this gene, as shown by Northern analysis. The GroEL1 chaperone is, therefore, dispensable in C. glutamicum. On the other hand, GroEL2 appears to be essential for growth. Based on these results, the role of the duplicate groEL1 and groEL2 genes is analyzed. Corynebacterium glutamicum (initially named Micrococcus glutamicus) was isolated from a soil sample of the Ueno Zoo in Tokyo as a high producer of glutamic acid (22). The type strain Kyowa Hakko Kogyo strain 534 was reclassified as C. glutami-cum (37) and deposited as ATCC 13032. A large number of mutants derived from C. glutamicum ATCC 13032 have been obtained in several laboratories and used for the industrial production of L-glutamic acid, L-lysine, and L-threonine. Due to its industrial relevance, a large re-search effort for the last two decades has focused on the mo