Chlorarachniophytes are amoebold algae with unusual chloroplasts. Instead

The chromosome of Bacillus subtilis codes for seven extracytoplasmic function sigma factors the activity of which is modulated normally by a cognate anti-sigma factor. While inducing factors and genes for four of them (sigma(M), sigma(W), sigma(X), and sigma(Y)) have been identified, those of the remaining three sigma factors including sigma(V) remain elusive. The objective of the present study was the unequivocal identification of its anti-sigma factor and of genes controlled by sigma(V). In many cases reported so far the gene coding for the anti-sigma factor is located immediately downstream of the gene coding for the sigma factor, and both form a bicistronic operon. We could show by two different experimental approaches that this is also the case for sigV and rsiV. Under conditions of overproduction of sigma(V), 13 genes could be identified being induced several-fold by the DNA macroarray technique. Induction of three of them was confirmed by Northern blots, and the potential promoter of sigV was identified by primer extension. This led to the deduction of a consensus sequence recognized by sigma(V).

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Cryptomonad algae and Chlorarachniophyta are evolutionary chimaeras derived from the engulfment of an eukaryotic phototrophic endosymbiont by a eukaryotic host cell. Although much reduced, the endosymbiont's eukaryotic plasmatic compartment still contains a nucleus, the so-called nucleomorph. These nucleomorphs carry the smallest known eukaryotic genomes. We have characterized the genomes of several cryptomonads and a Chlorarachnion species by means of PFGE (pulsed-field gel electrophoresis). Hybridization studies with small subunit rDNA were used to identify the nucleomorph chromosomes. We also performed hybridization experiments with an hsp70 probe to estimate the distribution of this gene among the different algal species. The evolutionary, genetical, and physiological implications of our studies are discussed. A model on the possible function of the nucleomorph hsp70 gene products is presented.