Saccharomyces cerevisiae prion [PSI ] is a self‐propagating isoform of the eukaryotic release factor eRF3 (Sup35p). Sup35p consists of the evolutionary conserved release factor domain (Sup35C) and two evolutionary variable regions – Sup35N, which serves as a prion‐forming domain in S. cerevisiae, and Sup35M. Here, we demonstrate that the prion form of Sup35p is not observed among industrial and natural strains of yeast. Moreover, the prion ([PSI + ]) state of the endogenous S. cerevisiae Sup35p cannot be transmitted to the next generations via heterologous Sup35p or Sup35NM, originating from the distantly related yeast species Pichia methanolica. This suggests the existence of a ‘species barrier’ in yeast prion conversion. However, the chimeric Sup35p, containing the Sup35NM region of Pichia, can be turned into a prion in S. cerevisiae by overproduction of the identical Pichia Sup35NM. Therefore, the prion‐forming potential of Sup35NM is conserved in evolution. In the heterologous system, overproduction of Pichia Sup35p or Sup35NM induced formation of the prion form of S. cerevisiae Sup35p, albeit less efficiently than overproduction of the endogenous Sup35p. This implies that prion induction by protein overproduction does not require strict correspondence of the ‘inducer’ and ‘inducee’ sequences, and can overcome the ‘species barrier’.

Two novel delta-endotoxin gene families cry26 and cry28 from Bacillus thuringiensis ssp. ¢nitimus. Abstract Genes cry26Aa1 and cry28Aa1 were cloned from Bacillus thuringiensis ssp. finitimus strain B-1166 VKPM. This strain forms insecticidal crystal bodies either outside or inside the exosporium. The deduced amino acid sequence of the cry26Aa1 gene product included seven residues determined to be an Nterminal part of a chymotrypsin-treated delta-endotoxin isolated from the same strain. Earlier this protein was detected in both free and spore-associated types of crystals [Revina et al., Biokhimia (1999) in press]. Neither BtI nor BtII promoter sequences were found upstream of the open reading frames in both genes. Southern hybridization has shown that the surroundings of both genes at least 3 kb upstream and downstream of the open reading frames are unique. We suggest that the protein Cry26Aa1 in both types of crystal bodies is synthesized under the control of one and the same genomic locus. z 1999 Federation of European Biochemical Societies.

A pair of highly degenerated primers was adapted to carry out a single‐step PCR‐detection of any known and probably unknown cry genes of classes cry1, cry4 and cry9 encoding for 130 kDa protein δ‐endotoxins in the natural Bacillus thuringiensis i(BT) strains. The Southern hybridization of the product has demonstrated that essentially remote cry‐genes like cry1Aa and cry9A (cryIG) could be represented in the single amplificate if they are simultaneously present in the genome of the analyzed strain. Four genes were detected by the proposed scheme in the iBT ssp. galleriae 11‐67. One of them, gene cry1Ga1 was originally found and cloned using the PCR‐amplification product obtained from the genomic DNA of this strain as a probe. The new gene was completely identical to one cloned by B. Lambert (unpublished, EMBL accession number Z22510) and essentially related to cryIM (EMBL accession number Y09326), renamed according to the new nomenclature as cry1Ga2.

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