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Genetic analysis of cryIIIA gene expression in Bacillus thuringiensis

Alejandra Bravo^1,

Unité de Biochimie Microbienne, Centre National de la Recherche Scientifique URA 1300, Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris Cedex 15, France
Laboratoire de Lutte Biologique, Institut National de Recherche Agronomique, La Minière, 78285 Guyancourt Cedex, France

³Author for correspondence: Sylvie Salamitou. Tel: +33 1 45 68 88 12. Fax: +33 1 45 68 89 38.

ABSTRACT

The Bacillus thuringiensis (Bt) cryIIIA gene is regulated by a different mechanism from that of most of the other cry genes. Its expression begins during late-exponential growth and not during sporulation as for the other classes of cry genes. Moreover, in Bacillus subtilis, cryIIIA expression is independent of the major sporulation-specific sigma factors and is increased in a spo0A genetic background. We used IacZ fusions and primer-extension analysis to follow the time-course of cryIIIA transcription in Bt wild-type and in various Spo_- genetic backgrounds (spo0A, sigE and sigK) cryIIIA was activated from the end of vegetative growth to stage II of sporulation (t₃) in the wild-type strain. Thereafter, transcription from the same promoter continued, at a decreasing rate, until the end of stage III. In the spo0A mutant strain, the same promoter was activated for at least 15 h during the stationary phase. cryIIIA activation in the sigK genetic background was similar to that in the wild-type but was extended in a sigE mutant strain. Thus cryIIIA expression in Bt is not directly dependent on the major sporulation-specific sigma factors. Furthermore, an event linked with the s^E-dependent period of sporulation ends cryIIIA activation, although transcription of this gene does not switch off before the end of stage III.

Present address: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca 62271, Mor., Mexico.

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