Comment on ‘Duplicated sporulation genes in bacteria’ by J. Errington, P. Fort and J. Mandelstam (FEBS Letters 188 (1985) 184‐188)

We recently presented a model for the structural organization of bacterial sigma factors based on a thorough comparison of available sequences [ 11.The major sigma factor of Escherichia coli, a", its Bacillus subtilis vegetative counterpart, t3, the E. coli heat shock regulatory protein encoded by the htpR gene and the product of the B. subtilis sporulation-essential spoIIG gene, share common characteristics: a highly conserved internal domain proposed to interact with core RNA polymerase and a carboxy-terminal region postulated to be involved in promoter recognition.In their recent article, Errington et al. [2] identify in the previously published sequence of the B. subtilis spoIIAC gene [3] a region exhibiting homology with known sigma factors.This region corresponds to the internal domain conserved in bacterial sigma factors [l] which was also the first one to be noticed in the SpoIIG sequence [4].However, no homology can be found in the carboxy-terminal region of the spoIIAC product with the postulated DNAbinding domain of the other sigma factors, a serious discrepancy with our model.Therefore we undertook a careful examination of the published spoIIAC sequence [3].This study revealed that shifting the reading frame in the distal part of the spoIIAC sequence by addition of one extra nucleotide at two different locations extended the spoIIAC coding sequence by 60 amino acids and restored the missing homologous domain.