Twin-arginine translocation pathway in Streptomyces lividans.

The recently discovered bacterial twin-arginine translocation (Tat) pathway was investigated in Streptomyces lividans, a gram-positive organism with a high secretion capacity. The presence of one tatC and two hcf106 homologs in the S. lividans genome together with the several precursor proteins with a twin-arginine motif in their signal peptide suggested the presence of the twin-arginine translocation pathway in the S. lividans secretome. To demonstrate its functionality, a tatC deletion mutant was constructed. This mutation impaired the translocation of the Streptomyces antibioticus tyrosinase, a protein that forms a complex with its transactivator protein before export. Also the chimeric construct pre-TorA-23K, known to be exclusively secreted via the Tat pathway in Escherichia coli, could be translocated in wild-type S. lividans but not in the tatC mutant. In contrast, the secretion of the Sec-dependent S. lividans subtilisin inhibitor was not affected. This study therefore demonstrates that also in general in Streptomyces spp. the Tat pathway is functional. Moreover, this Tat pathway can translocate folded proteins, and the E. coli TorA signal peptide can direct Tat-dependent transport in S. lividans.

Sulfate assimilation in Aspergillus terreus: analysis of genes encoding ATP-sulfurylase and PAPS-reductase.

Two genes for the sulfate assimilation pathway in Aspergillus terreus were cloned. The genes sAT (coding for PAPS-reductase) and sCT (coding for ATP-sulfurylase) form a small gene cluster. Both genes are similar to their homologs in A. nidulans (sA and sC), Penicillium chrysogenum (aps) and Saccharomyces cerevisiae (MET3 and MET16). In the coding sequence of the sCT gene, a typical non-functional APS-kinase-like domain is present. The sCT gene is expressed in A. nidulans, but its expression there is less sensitive to methionine level than in the original species. Two regions 5' upstream of sAT were found to be similar to those of sA.