Molecular cloning and sequence analysis of the crtB gene of Thermus thermophilus HB27, an extreme thermophile producing carotenoid pigments

We have cloned and sequenced a 1.5-kb chromosomal fragment of Thermus thermophilus which promoted the overproduction of carotenoids in T. thermophilus. An open reading frame (ORF-A) coding for a polypeptide with 289 amino acids was responsible for carotenoid overproduction. The putative ORF-A protein showed significant homology with the amino acid sequences of crtB gene products (phytoene syntheses) of other microorganisms. The clone containing the ORF-A on a multicopy plasmid produced about three times as much carotenoid as that produced by the host strain, suggesting that the crtB gene product is a rate-limiting enzyme for carotenoid biosynthesis in T. thermophilus.